Method for making a microstructure by surface micromachining

ABSTRACT

Various methods for forming surface micromachined microstructures are disclosed. One aspect relates to executing surface micromachining operation to structurally reinforce at least one structural layer in a microstructure. Another aspect relates to executing the surface micromachining operation to form a plurality of at least generally laterally extending etch release channels within a sacrificial material to facilitate the release of the corresponding microstructure.

FIELD OF THE INVENTION

[0001] The present invention generally relates to making amicrostructure by surface micromachining. One aspect relates to making astructurally reinforced microstructure to provide a flatter profile onone or more of its structural layers. Another aspect relates toproviding a plurality of at least generally laterally extending etchrelease channels to facilitate the release of the microstructure fromthe substrate.

BACKGROUND OF THE INVENTION

[0002] There are a number of microfabrication technologies that havebeen utilized for making microstructures (e.g., micromechanical devices,microelectromechanical devices) by what may be characterized asmicromachining, including LIGA (Lithographie, Galvonoformung,Abformung), SLIGA (sacrificial LIGA), bulk micromachining, surfacemicromachining, micro electrodischarge machining (EDM), lasermicromachining, 3-D stereolithography, and other techniques. Bulkmicromachining has been utilized for making relatively simplemicromechanical structures. Bulk micromachining generally entailscutting or machining a bulk substrate using an appropriate etchant(e.g., using liquid crystal-plane selective etchants; using deepreactive ion etching techniques). Another micromachining technique thatallows for the formation of significantly more complex microstructuresis surface micromachining. Surface micromachining generally entailsdepositing alternate layers of structural material and sacrificialmaterial using an appropriate substrate which functions as thefoundation for the resulting microstructure. Various patterningoperations may be executed on one or more of these layers before thenext layer is deposited so as to define the desired microstructure.After the microstructure has been defined in this general manner, thevarious sacrificial layers are removed by exposing the microstructureand the various sacrificial layers to one or more etchants. This iscommonly called “releasing” the microstructure from the substrate,typically to allow at least some degree of relative movement between themicrostructure and the substrate. Although the etchant may be biased tothe sacrificial material, it may have some effect on the structuralmaterial over time as well. Therefore, it is generally desirable toreduce the time required to release the microstructure to reduce thepotential for damage to its structure.

[0003] Microstructures are getting a significant amount of attention inthe field of optical switches. Microstructure-based optical switchesinclude one or more mirror microstructures. Access to the sacrificialmaterial that underlies the support layer that defines a given mirrormicrostructure is commonly realized by forming a plurality of small etchrelease holes down through the entire thickness or vertical extent ofthe mirror microstructure (e.g., vertically extending/disposed etchrelease holes). The presence of these small holes on the upper surfaceof the mirror microstructure has an obvious detrimental effect on itsoptical performance capabilities. Another factor that may have an effecton the optical performance capabilities of such a mirror microstructureis its overall flatness, which may be related to the rigidity of themirror microstructure. “Flatness” may be defined in relation to a radiusof curvature of an upper surface of the mirror microstructure. Thisupper surface may be generally convex or generally concave. Knownsurface micromachined mirror microstructures have a radius of curvatureof no more than about 0.65 meters.

BRIEF SUMMARY OF THE INVENTION

[0004] The present invention is generally embodied in a method formaking a microstructure by surface micromachining. In this method, atleast one and more typically a plurality of at least generally laterallyextending etch release channels or conduits are formed within asacrificial material. This sacrificial material is used to fabricate themicrostructure on an appropriate substrate. At least some of thissacrificial material is removed when the microstructure is released fromthe substrate (and thereby encompassing the situation where all of thissacrificial material is removed).

[0005] A first aspect of the present invention is embodied in a methodfor making a microstructure by surface micromachining that includesforming a first structural layer over a sacrificial material. “Over”includes being deposited directly on the substrate or being deposited onan intermediate layer that is disposed between the subject sacrificiallayer and the substrate. “On” in contrast means that there is aninterfacing relation. In any case, a plurality of hollow etch releasepipes, channels, conduits, or the like extend at least generallylaterally through/within this sacrificial material. Lateral or the like,as used herein, means that the etch release conduits are disposed ororiented in a direction which is at least generally parallel with thesubstrate. Although the etch release conduits will typically extendlaterally at a constant elevation relative to the substrate, such neednot necessarily be the case. Ultimately, at least some of thesacrificial material is removed at least in part by allowing an etchantto flow through any and all of these hollow etch release conduits (andthereby encompassing the situation where all of this sacrificial layeris removed).

[0006] Various refinements exist of the features noted in relation tothe first aspect of the present invention. Further features may also beincorporated in the first aspect of the present invention as well. Theserefinements and additional features may exist individually or in anycombination. In one embodiment, at least one end of at least one etchrelease conduit may be disposed at least generally at the same radialposition as a perimeter of the first structural layer. Hereafter, “atleast generally at the same radial position” in relation to any end ofany etch release conduit or structure used to define the same meanswithin 50 μm of the radial position of the perimeter of the relevantstructural layer in one embodiment, more preferably within 25 μm of theradial position of the perimeter of the relevant structural layer inanother embodiment, and even more preferably at the same radial positionas the perimeter of the relevant structural layer. As such, the etchantdoes not have to etch in from the perimeter “too far” beforeencountering an open end of one or more etch release conduits associatedwith the first aspect. Reducing the time required for the etchant toreach the etch release conduits should at least to a point reduce theoverall time for accomplishing the release of the microstructure fromthe substrate.

[0007] Various layouts of the plurality of etch release conduits in thenoted lateral dimension may be utilized in relation to the first aspect.In one embodiment, each of the plurality of etch release conduits may bedisposed in non-intersecting relation, in another embodiment theplurality of etch release conduits are disposed in at leastsubstantially parallel relation, and in yet another embodiment at leastsome of the etch release conduits intersect. The plurality of etchrelease conduits may extend at least generally toward (and therebyincluding to) a common point, such as one that corresponds with a centerof the first structural layer in the lateral dimension. All etch releaseconduits need not extend the same distance toward this common point,although such may be the case. Some of the plurality of etch releaseconduits may extend at least generally toward (and thereby including to)a first common point (e.g., one that corresponds with a center of thefirst structural layer in the lateral dimension), while some of theplurality of etch release conduits may extend toward a different commonpoint. The plurality of etch release conduits may also extend in thelateral dimension in a variety of configurations. In one embodiment, theplurality of etch release conduits are at least generally axiallyextending, while in another embodiment the plurality of etch releaseconduits are non-linear (e.g., in a sinusoidal configuration that is atleast generally parallel with the substrate).

[0008] In one embodiment of the first aspect, the laterally extendingetch release conduits are completely defined before the stack thatincludes the microstructure being fabricated by the methodology of thefirst aspect is exposed to a release etchant for removing the firstsacrificial layer. One particularly desirable application for the firstaspect is in the formation of a mirror microstructure or multiple mirrormicrostructures for a surface micromachined optical system that has atleast some degree of movement relative to the first substrate. Becauseof the presence of the plurality of laterally extending etch releaseconduits, there is no need to have a plurality of etch release aperturesor holes that extend entirely down through the entire vertical extent ofthe first structural layer to remove the sacrificial material thatdirectly underlies this first structural layer. That is, there is noneed for a plurality of vertically disposed etch release apertures, with“vertical” being at least generally opposite “lateral.” As such, theupper surface of the first structural layer retains a very smoothsurface that lacks any such vertically disposed etch release apertures,which makes the microstructure that is made by the methodology of thefirst aspect particularly suited for use in optical applications. Thisis true whether the upper surface of the first structural layer is theactual optical surface for the mirror microstructure, or whether a filmor other layer is deposited on the first structural layer to providemore desirable optical properties/characteristics.

[0009] The sacrificial material that directly underlies the firststructural layer used by the first aspect may actually be defined by thesequential deposition of multiple sacrificial layers, one on top of theother. That is, a lower portion of this sacrificial material may beformed as one layer, and an upper portion of this sacrificial materialmay be subsequently formed in overlying relation. Consider a case wherea first sacrificial layer is formed over the first substrate, and wherea first intermediate layer is formed on this first sacrificial layer.The first intermediate layer may be patterned to define a firstsubassembly (e.g., a plurality of strips). Portions of the firstsacrificial layer are exposed by a patterning of the first intermediatelayer to define the first subassembly. An upper portion of the firstsacrificial layer (i.e., something less than the entirety of the firstsacrificial layer) may be etched an amount after this patterning suchthat at least part of the first sacrificial layer that underlies atleast part of the first subassembly is removed (e.g., using a timedetch). The first subassembly may be disposed directly on the firstsacrificial layer, directly on a structural layer, or directly on boththe first sacrificial layer and a structural layer (e.g., for the casewhere there is both a sacrificial material and a structural material atthe same level within a stack which contains the microstructure beingfabricated by the methodology of the subject first aspect).

[0010] The “gap” that now exists between the first subassembly and thatportion of the etched first sacrificial layer that is directly beneaththe first subassembly may be characterized as an undercut. A secondsacrificial layer may be formed on at least the first sacrificial layer.One could characterize this as “backfilling.” Notwithstanding thischaracterization of the backfilled sacrificial material as a “secondsacrificial layer”, the first and second sacrificial layers may in factbe indistinguishable from each other and may in effect define acontinuous structure. Nonetheless, the sacrificial material that hasbeen characterized as the second sacrificial layer will not fill theentire extent of each of the undercuts. This failure to fill theundercuts defines the plurality of etch release conduits that areassociated with the first aspect of the present invention. One couldvisualize that the first subassembly acts as an umbrella of sorts thatprevents the material that has been characterized as the secondsacrificial layer from totally filling the noted undercuts that areprotected by the first subassembly. Typically the second sacrificiallayer will also cover the first subassembly. In this case and possiblyin other instances during the fabrication of the microstructureassociated with the first aspect, it may be desirable to planarize anupper surface of a given layer before depositing the next layer thereon.One appropriate technique for providing this planarization function ischemical mechanical polishing.

[0011] The first subassembly may be a reinforcing structure for thefirst structural layer, in which case the first subassembly would existin the microstructure that is defined by the methodology of the firstaspect. Reinforcement may be provided by structurally interconnectingthe first structural layer with the first subassembly through theabove-noted second sacrificial layer which may be deposited on the firstsubassembly in addition to the first sacrificial layer as noted. Furtherreinforcement of the first structural layer may be accomplished bystructurally interconnecting the first subassembly with a structurallayer that underlies the first sacrificial layer. In both cases, theactual reinforcement structure could be in the form of a plurality ofposts or columns that are disposed in spaced relation, in the form of aplurality of at least generally laterally extending ribs or rails, or inthe form of a grid-like reinforcement structure.

[0012] The first subassembly need not remain in the microstructure thatmay be defined by the methodology of the first aspect. That is, thefirst subassembly need not be part of the final microstructure that isultimately fabricated by the methodology of the first aspect. In thiscase, the only purpose of the first subassembly would be to at leastassist in the formation of the plurality of etch release conduits thatare associated with the first aspect of the present invention. This“temporary” first subassembly may be in the form of a plurality of railsthat are formed on or in a sacrificial material that is used in themethodology of the first aspect. Removal of the first subassembly fromthe final microstructure being made by the subject first aspect may bedesirable in order to retain a low mass for this microstructure (e.g.,in an upper structural layer of such a microstructure).

[0013] One way in which the first subassembly may be removed oralleviated from the final microstructure being made by the first aspectof the present invention is to form the first subassembly from amaterial that would be etched away along with the various sacrificiallayers, although possibly at a different rate. Appropriate materials forthe first subassembly in this case include silicon nitride,poly-silicon-germanium, or any other material that is soluble in therelease etch or other etchant that will not have an adverse effect onany of the structural layers that may be included in the microstructurebeing made by the methodology of the subject first aspect. Having thefirst subassembly be of a reduced thickness may also contribute to thefirst subassembly being removed along with the sacrificial materialwithin a desired time when releasing the microstructure made by themethodology of the first aspect. In one embodiment where the firstsubassembly is formed from silicon nitride and in the form of aplurality of strips, the first subassembly has a thickness or verticalextent of typically less than about 1,500 Å for this purpose.

[0014] Another option for creating the plurality of at least generallylaterally extending etch release channels in accordance with the firstaspect entails forming a first intermediate layer that will underlie thefirst sacrificial layer. This first intermediate layer may be patternedto define a plurality of at least generally laterally extending stripsthat are disposed in non-intersecting relation over at least a portionof their length. These strips are spaced relatively close to each othersuch that when the first sacrificial layer is deposited on the firstintermediate layer, the sacrificial material is unable to entirely fillthe space between the adjacent strips. More specifically, an upperportion of the space between adjacent strips will “close off” during thedeposition of the material that defines the first sacrificial layerbefore a lower portion of the space between the adjacent strips has hada chance to be filled with the material that defines the firstsacrificial layer. Each “unfilled” void between adjacent pairs of stripsdefines one of the plurality of etch release channels referenced inrelation to the first aspect. The manner in which the voids are formedmay be characterized as “keyholing.” Keyholing in relation to the firstaspect is a result a relatively close spacing between adjacent strips inrelation to their thickness or vertical extent. In one embodiment, aratio of the height of these strips to the spacing between adjacentstrips is at least about 1:1.

[0015] Further options exist for creating the plurality of at leastgenerally laterally extending etch release channels in accordance withthe first aspect. One way is to use multiple, different etchants. Afirst etchant that is not selective to the first sacrificial layer maybe used to form the plurality of at least generally laterally extendingetch release channels. A second, different etchant that is selective tothe first sacrificial layer may thereafter be directed through theplurality of at least generally laterally extending etch releasechannels or conduits (again created/defined by the first etchant) toremove the first sacrificial layer. The first etchant may be selectiveto a material that forms a plurality of at least generally laterallyextending etch release rails that are embedded or encased within thefirst sacrificial layer or at least in a sacrificial material. Anyappropriate layout may be utilized for these plurality of at leastgenerally laterally extending etch release rails, including a pluralityof separate and discrete etch release rails, a network or grid ofinterconnected etch release rails, or some combination thereof.

[0016] The intermediate structure in the fabrication of themicrostructure in accordance with the first aspect may be characterizedas a stack, and includes the various layers that are sequentiallydeposited on the substrate, and thereafter possibly patterned. Thisstack includes an exterior surface that is opposite the first substrate.Access to at least one of the etch release rails in the above-noted twoetchant example may be provided by a first runner that extends from thisexterior surface of the stack and at least generally toward the firstsubstrate to a level such that it may structurally interconnect with atleast one of the plurality of etch release rails. The same material thatdefines the etch release rails may define this first runner, such thatthe first etchant will first remove the first runner, and then each etchrelease rail that is structurally interconnected therewith (eitherdirectly or indirectly). Multiple first runners may be provided foraccessing the plurality of etch release rails, multiple etch releaserails may be accessed by a single first runner, or some combinationthereof.

[0017] A second aspect of the present invention is embodied in a methodfor making a microstructure in which a plurality of at least generallylaterally extending etch release channels or conduits are formed withina sacrificial material that is used to build/assemble the microstructureon an appropriate substrate, but which is at least in part removed whenthe microstructure is released from this substrate. These etch releasechannels do not exist until the release of the microstructure isinitiated in the second aspect. In this regard, the method of the secondaspect includes forming a first intermediate layer on top of a firstsacrificial layer or possibly on top of the substrate. This firstintermediate layer is patterned to define a plurality of at leastgenerally laterally extending first strips that sit on top of the firstsacrificial layer. A second sacrificial layer is thereafter deposited onthat portion of the first sacrificial layer which was exposed by thepatterning of the first intermediate layer so as to be disposed at leastalongside the first strips. Although not fundamentally required by thesecond aspect, the second sacrificial layer may also be disposed on topof the first strips as well. In any case, a first structural layer isformed on top of the second sacrificial layer. Both the first and secondsacrificial layers are removed at least in part using an appropriateetchant. Generally, those portions of the second sacrificial layer thatinterface with or are disposed adjacent to the first strips etch at agreater rate than other portions of the second sacrificial layer whicheffectively defines a plurality of at least generally laterallyextending etch release pipes, channels, conduits or the like. Aplurality of hollow and at least generally laterally extending etchrelease channels or conduits (e.g., disposed at least generally parallelwith an upper surface of the first substrate) are thereby formed in thesecond sacrificial layer by this differential etch rate. Although theseetch release conduits will typically be disposed at a constant elevationrelative to the substrate, such need not necessarily be the case.Ultimately, at least part of the second sacrificial layer, as well asthe first sacrificial layer, are removed at least in part by allowing anetchant to flow through any and all of the noted conduits after theformation of the same in the releasing operation (and therebyencompassing the situation where all of the first and second sacrificiallayers are removed, as well as the first intermediate layer if the sameis not a structural material as discussed below).

[0018] Various refinements exist of the features noted in relation tothe second aspect of the present invention. Further features may also beincorporated in the second aspect of the present invention as well.These refinements and additional features may exist individually or inany combination. The noted differential etch rate is believed to bebased upon the density of that portion of the second sacrificial layerin proximity to the first strips being less than a density of theremainder of the second sacrificial layer, as well as a density of thefirst sacrificial layer as well for that matter. The differentialdensity is due to the sticking characteristics of the depositing atomsor molecules, which depends on the characteristics of the depositiontechnique. For example, the density of add-on molecules in aplasma-enhanced chemical vapor deposition (PECVD) system depends ondirectional orientation of the surface to the plasma body. In this way,atoms or molecules striking the surface have different energy availableto them to aid in their positioning in low-energy (i.e. high-density)positions on the surface.

[0019] In one embodiment of the second aspect, at least one end of atleast one first strip may be disposed at least generally at the sameradial position as a perimeter of the first structural layer. Since thefirst strips effectively define the etch release conduits, at least oneend of at least one etch release conduit may be disposed at this sameradial position as well. As such, the etchant does not have to etch infrom the perimeter “too far” before encountering a region that will havea higher etch rate, and that again defines a corresponding etch releaseconduit. The parameters mentioned above in relation to the first aspectregarding this feature are equally applicable to this second aspect.

[0020] Various layouts of the plurality of first strips (and thereby theetch release conduits) in the noted lateral dimension may be utilized inaccordance with the second aspect. In one embodiment, each of theplurality of at least generally laterally first strips are furtherdisposed in non-intersecting relation, in another embodiment each of theplurality of first strips are disposed in at least substantiallyparallel relation, and in yet another embodiment at least some of thefirst strips intersect. The plurality of first strips may extend atleast generally toward (and thereby including to) a common point, suchas one that corresponds with a center of the first structural layer inthe lateral dimension. All of the first strips need not extend the samedistance toward this common point, although such may be the case. Someof the plurality of strips may extend at least generally toward (andthereby including to) a first common point (e.g., one that correspondswith a center of the first structural layer in the lateral dimension),while some of the plurality of first strips may extend toward adifferent common point. The plurality of first strips utilized by thesecond aspect may also extend in the lateral dimension in a variety ofconfigurations. In one embodiment, the plurality of first strips are atleast generally axially extending, while in another embodiment theplurality of first strips are non-linear (e.g., in a sinusoidalconfiguration within a plane that is parallel with the substrate).

[0021] One particularly desirable application for the second aspect isin the formation of a mirror microstructure or multiple mirrormicrostructures for a surface micromachined optical system that has atleast some degree of movement relative to the first substrate. Becauseof the different etch rates that result from the way in which themicrostructure is made by the methodology of the second aspect, there isno need to have a plurality of vertically disposed etch releaseapertures that extend down entirely through the second structural layerto release the mirror microstructure from the first substrate by theremoval of the underlying first and second sacrificial layers. As such,the upper surface of the second structural layer retains a very smoothsurface that lacks any such vertically disposed etch release apertures,which makes the microstructure that is made by the methodology of thesecond aspect particularly suited for use in optical applications. Thisis true whether the upper surface of the second structural layer is theactual optical surface for the mirror microstructure, or whether a filmor other layer is deposited on the second structural layer to providemore desirable optical properties/characteristics.

[0022] Typically the second sacrificial layer will also cover the firststrips (again, formed from the first intermediate layer) such that theyare effectively embedded between the first and second sacrificiallayers. In this case, it may be desirable to planarize an upper surfaceof the second sacrificial layer before depositing the first structurallayer thereon. It may also be desirable to planarize an upper surface ofother layers within the microstructure made in accordance with themethodology of the second aspect as well before depositing another layerthereon. One appropriate technique for executing this planarizationfunction is chemical mechanical polishing.

[0023] The first strips may be a reinforcing structure for the firststructural layer and would then exist in the microstructure that is madeby the methodology of the second aspect. Reinforcement may be providedby structurally interconnecting the first structural layer with thefirst strips through the above-noted second sacrificial layer which maybe deposited on the first strips in addition to the first sacrificiallayer as noted. Further reinforcement of the first structural layer maybe accomplished by structurally interconnecting the first strips with astructural layer that underlies the first sacrificial layer and therebythe first structural layer. In both cases, the actual reinforcingstructure could be in the form of a plurality of posts or columns thatare disposed in spaced relation, in the form of a plurality of at leastgenerally laterally extending ribs or rails, or in the form of agrid-like reinforcement structure.

[0024] A third aspect of the present invention is embodied in a methodfor making a surface micromachined microstructure. A first sacrificiallayer is formed over a first substrate in a manner so as to define aplurality of at least generally laterally extending low density regionstherein. A first structural layer is thereafter formed over the firstsacrificial layer. The release of the first structural layer from thefirst substrate is affected by removing the first sacrificial layer withan appropriate etchant. The etching rate within the low density regionsof the first sacrificial layer is greater than in other regions of thefirst sacrificial layer.

[0025] Various refinements exist of the features noted in relation tothe third aspect of the present invention. Further features may also beincorporated in the third aspect of the present invention as well. Theserefinements and additional features may exist individually or in anycombination. The higher etch rate in the low density regions of thefirst sacrificial layer may define a plurality of at least generallylaterally extending etch release pipes, channels, conduits, or the like,which in turn should reduce the time required to completely release themicrostructure from the first substrate. Although the low densityregions will typically be disposed at a constant elevation relative tothe substrate, such need not be the case.

[0026] In one embodiment of the third aspect, at least one end of atleast one low density region may be disposed at least generally at thesame radial position as a perimeter of the first structural layer. Sincethe low density regions effectively define the etch release conduits, atleast one end of at least one etch release conduit may be disposed atthis same radial position as well. As such, the etchant does not have toetch in from the perimeter “too far” before encountering a low densityregion for definition of an etch release conduit(s). The parametersmentioned above in relation to the first aspect regarding this featureare equally applicable to this third aspect.

[0027] Various layouts of the plurality of low density regions, andthereby the etch release conduits, in the noted lateral dimension may beutilized in accordance with the third aspect. In one embodiment, each ofthe plurality of at least generally laterally extending low densityregions are disposed in non-intersecting relation, in another embodimenteach of the plurality of low density regions are disposed in at leastsubstantially parallel relation, and in yet another embodiment at leastsome of the low density regions intersect. The plurality of low densityregions may extend at least generally toward (and thereby including to)a common point, such as one that corresponds with a center of the firststructural layer in the lateral dimension. All of the low densityregions need not extend the same distance toward this common point,although such may be the case. Some of the plurality of low densityregions may extend at least generally toward (and thereby including to)a first common point (e.g., one that corresponds with a center of thefirst structural layer in the lateral dimension), while some of theplurality of low density regions may extend toward a different commonpoint. The plurality of low density regions utilized by the third aspectmay also extend in the lateral dimension in a variety of configurations.In one embodiment, the plurality of low density regions are at leastgenerally axially extending, while in another embodiment the pluralityof low density regions are nonlinear (e.g., in a sinusoidalconfiguration within a plane that is at least generally parallel withthe substrate).

[0028] One way in which the low density regions associated with thethird aspect may be formed is by forming a second sacrificial layer overthe first substrate, and then patterning the same to define a pluralityof at least generally laterally extending etch release conduitapertures. Each of these etch release conduit apertures is defined byfirst and second sidewalls that are disposed in spaced relation to eachother. The first sacrificial layer is formed such that the material ofthe first sacrificial layer is deposited within these etch releaseconduit apertures. The first sacrificial layer may be deposited on thetop of the second sacrificial layer as well. In any case, the lowdensity regions associated with the third aspect will thereby existalong the first and second sidewalls of each of the etch release conduitapertures.

[0029] One advantage of the above-noted method for defining the lowdensity regions in accordance with the third aspect, and thereby fordefining a plurality of etch release channels, is that a layout of thelow density regions may define a network or grid-like structure or suchthat a plurality of these low density regions cross and/or areinterconnected in some manner. For instance, the patterning of thesecond sacrificial layer could define a repeating pattern ofinterconnected “diamonds,” a honeycomb or honeycomb-like structure, orthe like. This ability to define a network could further enhance thedistribution of the etchant during the release of the first structurallayer from the first substrate. Another advantage of this particularmethod for defining the low density regions, and thereby for defining aplurality of etch release channels, is that the same does not requirethe use of any structural layer or material for the formation thereof.Therefore, this particular embodiment of the third aspect could be usedto enhance the release of a simple, single structural layer in amicrostructure.

[0030] The above-noted methodology for defining the low density regionsin accordance with the third aspect may also be utilized wherestructural reinforcement of the first structural layer is desired.Structural reinforcement of the first structural layer may be realizedby having an appropriate reinforcement structure cantilever downwardlyfrom a lower surface of the first structural layer. Another way tostructurally reinforce the first structural layer is to structurallyinterconnect the first structural layer with an underlying structurallayer. The only limitation on the use of any such reinforcementstructure is that it should not extend downwardly through any of thenoted low density regions so as to cut off any etch release channels.This may be done in variety of manners. Consider the case where thesecond sacrificial layer is patterned in the form of a honeycomb. Aplurality of columns or posts could extend downwardly from the firststructural layer through the “closed cell” portions of the honeycombwithout intersecting with any of the low density regions which definethe profile of the honeycomb (in plan view).

[0031] Notwithstanding the advantages of the above-noted method forforming the low density regions in accordance with the third aspect,these low density regions may also be defined in the manner discussedabove in relation to the second aspect. Therefore, those featuresdiscussed above in relation to the second aspect may be used in thisthird aspect as well.

[0032] A fourth aspect of the present invention is embodied in a methodfor making a surface micromachined microstructure. A first sacrificiallayer is formed over a first substrate. A first structural layer isformed over the first sacrificial layer. The release of the firststructural layer from the first substrate is affected by what may becharacterized as a two step etch. In this regard, a first etchant may beused to form a plurality of at least generally laterally extending etchrelease channels or conduits within the first sacrificial layer or so asto otherwise be embedded within a sacrificial material. A second,different etchant that is selective to the first sacrificial layer maythereafter be directed through the plurality of at least generallylaterally extending etch release channels (again created/defined by thefirst etchant) to remove the first sacrificial layer.

[0033] Various refinements exist of the features noted in relation tothe fourth aspect of the present invention. Further features may also beincorporated in the fourth aspect of the present invention as well.These refinements and additional features may exist individually or inany combination. The first etchant may be selective to a material thatforms a plurality of at least generally laterally extending etch releaserails that are embedded or encased within the first sacrificial layer orat least in a sacrificial material. Any appropriate layout may beutilized for these plurality of at least generally laterally extendingetch release rails, including a plurality of separate and discrete etchrelease rails, a network or grid of interconnected etch release rails,or some combination thereof.

[0034] The intermediate structure in the fabrication of themicrostructure in accordance with the fourth aspect may be characterizedas a stack, and includes the various layers that are sequentiallydeposited on the substrate, and thereafter possibly patterned. Thisstack includes an exterior surface that is opposite the first substrate.Access to at least one of the noted etch release rails may be providedby a first runner that extends from this exterior surface of the stackand at least generally toward the substrate to a level such that it mayinterconnect with at least one of the plurality of etch release rails.The same material that defines the etch release rails may define thisfirst runner, such that the first etchant will first remove the firstrunner, and then each etch release rail interconnected therewith.Multiple first runners may be provided for accessing the plurality ofetch release rails, multiple etch release rails may be accessed by asingle first runner, or some combination thereof.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0035]FIG. 1A is a plan view of one embodiment of surface micromachinedoptical system that includes a movable mirror microstructure.

[0036]FIG. 1B is a plan view of another embodiment of a surfacemicromachined optical system that includes a movable mirrormicrostructure.

[0037]FIG. 1C is a bottom view of the surface micromachined opticalsystem of FIG. 1B.

[0038]FIG. 2A is a cross-sectional view of one embodiment of a mirrormicrostructure that may be used in a surface micromachined opticalsystem.

[0039]FIG. 2B is a cross-sectional view of a portion of the mirrormicrostructure of FIG. 2A with an optical coating thereon.

[0040]FIG. 3 is a cross-sectional view of the mirror microstructure ofFIG. 2A along line 3-3.

[0041]FIG. 4 is a cross-sectional view of another embodiment of a mirrormicrostructure that may be used in a surface micromachined opticalsystem.

[0042]FIG. 5 is a cross-sectional view of another embodiment of a mirrormicrostructure that may be used in a surface micromachined opticalsystem.

[0043]FIG. 6 is a cross-sectional view of the mirror microstructure ofFIG. 5 taken along line 6-6, as well as of the mirror microstructure ofFIG. 7 taken along line 6-6.

[0044]FIG. 7 is a cross-sectional view of another embodiment of a mirrormicrostructure that may be used in a surface micromachined opticalsystem.

[0045]FIG. 8 is a cross-sectional view of the mirror microstructure ofFIG. 7 taken along line 8-8.

[0046]FIG. 9A is a cross-sectional view of another embodiment of amirror microstructure that may be used in a surface micromachinedoptical system.

[0047]FIG. 9B is a cross-sectional view of the mirror microstructure ofFIG. 9A taken along line 9B-9B.

[0048]FIG. 10A is a cross-sectional view of another embodiment of amirror microstructure that may be used in a surface micromachinedoptical system.

[0049]FIG. 10B is a cross-sectional view of the mirror microstructure ofFIG. 10A taken along line 10B-10B.

[0050]FIG. 10-C is a cross-sectional view of the mirror microstructureof FIG. 10A taken along line 10C/D-10C/D.

[0051]FIG. 10D is a cross-sectional view of a variation of the mirrormicrostructure of FIG. 10A taken along line 10C/D-10C/D.

[0052]FIG. 11A is a cross-sectional view of another embodiment of a raillayout for structural reinforcement and/or rapid etch release.

[0053]FIG. 11B is a cross-sectional view of another embodiment of a raillayout for structural reinforcement and/or rapid etch release.

[0054]FIG. 11C is a cross-sectional view of another embodiment of a raillayout for structural reinforcement and/or rapid etch release.

[0055]FIG. 11D is a cross-sectional view of another embodiment of a raillayout for structural reinforcement and/or rapid etch release.

[0056]FIG. 11E is a cross-sectional view of another embodiment of a raillayout for structural reinforcement and/or rapid etch release.

[0057]FIG. 11F is a cross-sectional view of another embodiment of a raillayout for structural reinforcement and/or rapid etch release.

[0058] FIGS. 12A-M are sequential views of one embodiment for making oneembodiment of a microstructure for a surface micromachined system.

[0059] FIGS. 13A-M are sequential views of another embodiment for makingone embodiment of a microstructure for a surface micromachined system.

[0060] FIGS. 14A-F are sequential views of another embodiment for makingone embodiment of a microstructure for a surface micromachined system.

[0061] FIGS. 15A-G are sequential views of another embodiment for makingone embodiment of a microstructure for a surface micromachined system.

[0062] FIGS. 16A-C are sequential views of another embodiment for makingone embodiment of a microstructure for a surface micromachined system.

[0063] FIGS. 17A-G are sequential views of another embodiment for makingone embodiment of a microstructure for a surface micromachined system.

[0064]FIG. 18A is a top/plan view of one embodiment of an etch releaseconduit aperture grid that may be defined using the methodology of FIG.17A-G, and at a point in time in the process corresponding with FIG. 17Band along line 18A-18A in FIG. 17B.

[0065]FIG. 18B is a cutaway view of the embodiment of FIG. 18A, at apoint in time in the process corresponding with FIG. 17F and along line18B-18B in FIG. 17F.

[0066] FIGS. 19A-F are sequential views of another embodiment for makingone embodiment of a microstructure for a surface micromachined system,and which uses the same technique for forming a plurality of etchrelease conduits as the method of FIGS. 17A-G.

[0067] FIGS. 20A-D are sequential views of another embodiment for makingone embodiment of a microstructure for a surface micromachined system.

DETAILED DESCRIPTION OF THE INVENTION

[0068] The present invention will now be described in relation to theaccompanying drawings which at least assist in illustrating its variouspertinent features. Surface micromachined microstructures and methods ofmaking the same are the general focus of the present invention. Varioussurface micromachined microstructures and surface micromachiningtechniques are disclosed in U.S. Pat. No. 5,783,340, issued Jul. 21,1998, and entitled “METHOD FOR PHOTOLITHOGRAPHIC DEFINITION OF RECESSEDFEATURES ON A SEMICONDUCTOR WAFER UTILIZING AUTO-FOCUSING ALIGNMENT”;U.S. Pat. No. 5,798,283, issued Aug. 25, 1998, and entitled “METHOD FORINTEGRATING MICROELECTROMECHANICAL DEVICES WITH ELECTRONIC CIRCUITRY;U.S. Pat. No. 5,804,084, issued Sep. 8, 1998, and entitled “USE OFCHEMICAL MECHANICAL POLISHING IN MICROMACHINING”; U.S. Pat. No.5,867,302, issued Feb. 2, 1999, and entitled “BISTABLEMICROELECTROMECHANICAL ACTUATOR”; and U.S. Pat. No. 6,082,208, issuedJul. 4, 2000, and entitled “METHOD FOR FABRICATING FIVE-LEVELMICROELECTROMECHANICAL STRUCTURES AND MICROELECTROMECHANICALTRANSMISSION FORMED, the entire disclosures of which are incorporated byreference in their entirety herein.

[0069] The term “sacrificial layer” as used herein means any layer orportion thereof of any surface micromachined microstructure that is usedto fabricate the microstructure, but which does not exist in the finalconfiguration. Exemplary materials for the sacrificial layers describedherein include undoped silicon dioxide or silicon oxide, and dopedsilicon dioxide or silicon oxide (“doped” indicating that additionalelemental materials are added to the film during or after deposition).The term “structural layer” as used herein means any other layer orportion thereof of a surface micromachined microstructure other than asacrificial layer and a substrate on which the microstructure is beingfabricated. Exemplary materials for the structural layers describedherein include doped or undoped polysilicon and doped or undopedsilicon. Exemplary materials for the substrates described herein includesilicon. The various layers described herein may be formed/deposited bytechniques such as chemical vapor deposition (CVD) and includinglowpressure CVD (LPCVD), atmospheric-pressure CVD (APCVD), andplasma-enhanced CVD (PECVD), thermal oxidation processes, and physicalvapor deposition (PVD) and including evaporative PVD and sputtering PVD,as examples.

[0070] In more general terms, surface micromachining can be done withany suitable system of a substrate, sacrificial film(s) or layer(s) andstructural film(s) or layer(s). Many substrate materials may be used insurface micromachining operations, although the tendency is to usesilicon wafers because of their ubiquitous presence and availability.The substrate is essentially a foundation on which the microstructuresare fabricated. This foundation material must be stable to the processesthat are being used to define the microstructure(s) and cannot adverselyaffect the processing of the sacrificial/structural films that are beingused to define the microstructure(s). With regard to the sacrificial andstructural films, the primary differentiating factor is a selectivitydifference between the sacrificial and structural films to thedesired/required release etchant(s). This selectivity ratio ispreferably several hundred to one or much greater, with an infiniteselectivity ratio being preferred. Examples of such a sacrificialfilm/structural film system include: various silicon oxides/variousforms of silicon; poly germanium/poly germanium-silicon; variouspolymeric films/various metal films (e.g., photoresist/aluminum);various metals/various metals (e.g., aluminum/nickel);polysilicon/silicon carbide; silicone dioxide/polysilicon (i.e., using adifferent release etchant like potassium hydroxide, for example).Examples of release etchants for silicon dioxide and silicon oxidesacrificial materials are typically hydrofluoric (HF) acid based (e.g.,undiluted or concentrated HF acid, which is actually 49 wt % HF acid and51 wt % water; concentrated HF acid with water; buffered HF acid (HFacid and ammonium fluoride)).

[0071] Only those portions of a surface micromachined microstructurethat are relevant to the present invention will be described herein.There may and typically will be other layers that are included in agiven surface micromachined microstructure, as well as in any systemthat includes such microstructures. For instance and in the case wherethe surface micromachined microstructures described herein are utilizedas a movable mirror microstructure in a surface micromachined opticalsystem, a dielectric isolation layer will typically be formed directlyon an upper surface of the substrate on which such a surfacemicromachined optical system is to be fabricated, and a structural layerwill be formed directly on an upper surface of the dielectric isolationlayer. This particular structural layer is typically patterned andutilized for establishing various electrical interconnections for thesurface micromachined optical system which is thereafter fabricatedthereon.

[0072] One embodiment of at least a portion of a surface micromachinedoptical system 2 is presented in FIG. 1A. The surface micromachinedoptical system 2 is fabricated on a substrate (not shown) and includesat least one microstructure in the form of a mirror microstructure 6.The surface micromachined optical system 2 may and typically willinclude multiple mirror microstructures 6 that are disposed/arranged inthe form of an array (not shown), although there may be applicationswhere only a single mirror microstructure 6 is required. The mirrormicrostructure 6 is interconnected with the substrate by a plurality ofsuspension springs 8. One end of each spring 8 is interconnected withthe mirror microstructure 6, while its opposite end is interconnectedwith a structural support 4 that is in turn interconnected with thesubstrate (possibly through one or more underlying structural layers,which is the configuration shown in FIG. 1A).

[0073] A lower electrode 10 is disposed below the mirror microstructure6 in spaced relation and is interconnected with the substrate as well.An electrical contact 12 a is interconnected with the lower electrode10, while an electrical contact 12 b is interconnected with the mirrormicrostructure 6. Appropriate voltages may be applied to both of theelectrical contacts 12 a, 12 b to move the mirror microstructure 6toward or away from the lower electrode 10 (and thereby the substrate)into a desired position to provide an optical function. This movement istypically at least generally perpendicular relative to the lowerelectrode 10 and the substrate. The mirror microstructure 6 is commonlyreferred to as a piston mirror based upon the described motion.

[0074] Another embodiment of at least a portion of a surfacemicromachined optical system 16 is presented in FIGS. 1B-C. The surfacemicromachined optical system 16 is fabricated on a substrate (not shown)and includes at least one microstructure in the form of a mirrormicrostructure 20. The surface micromachined optical system 16 may andtypically will include multiple mirror microstructures 20 that aredisposed/arranged in the form of an array (not shown), although theremay be applications where only a single mirror microstructure 20 isrequired. The mirror microstructure 20 is interconnected with thesubstrate by a pair of suspension springs 22. An imaginary line thatextends between the springs 22 defines an axis about which the mirrormicrostructure 20 may pivot. One end of each spring 22 is interconnectedwith the mirror microstructure 20, while its opposite end isinterconnected with a structural support 18 that is in turninterconnected with the substrate.

[0075] A pair of lower electrodes 24 are disposed below the mirrormicrostructure 20 and are interconnected with the substrate as well. Oneelectrode 24 a is associated with one side of the above-noted pivotaxis, while the electrode 24 b is associated with the opposite side ofthe above-noted pivot axis. There is one electrical contact 26 aelectrically interconnected with each lower electrode 24, while there isan electrical contact 26 b electrically interconnected with the mirrormicrostructure 20. Appropriate voltages may be applied to appropriateones of the contacts 26 to pivot the mirror microstructure 20 about itspivot axis in the desired direction and amount into a desired positionto provide an optical function.

[0076] Details regarding a particular configuration of a mirrormicrostructure in a surface micromachined optical system, such as forthe mirror microstructures 6 and 20 in the surface micromachined opticalsystems 2 and 16 of FIGS. 1A and 1B-C, respectively, are presented inFIGS. 2A and 3 in the form of a two-layered mirror microstructure 30.The mirror microstructure 30 is made on an appropriate substrate 54 bysurface micromachining techniques. Components of the mirrormicrostructure 30 include a first structural layer or support 34 that isspaced vertically upward relative to the substrate 54 (e.g., disposed ata higher elevation relative to the substrate 54), a second structurallayer or support 38 that is spaced vertically upward relative to thefirst structural layer 34 (e.g., disposed at a higher elevation relativeto the substrate 54), and a plurality of separate and discrete columnsor posts 50 that are disposed in spaced relation. The columns 50 extendbetween and fixedly interconnect the first structural layer 34 and thesecond structural layer 38 for providing structural reinforcement forthe microstructure and, more particularly, the second structural layer38. The columns 50 may be disposed in either equally spaced relation orthe spacing between adjacent columns 50 may vary in at least somemanner. Therefore, the second structural layer 38 and first structurallayer 34, along with the interconnecting columns 50, may be movedsimultaneously if acted upon by any interconnected actuator to provide adesired/required optical function.

[0077] An upper surface 46 of the second structural layer 38 is or mayinclude an optically reflective layer or film. That is, the materialsthat are used to define the second structural layer may provide thedesired/required optical properties/characteristics for the mirrormicrostructure 30. More typically a separate layer or film 48 (FIG. 2B)will be deposited on an upper surface 46 of the second structural layer38 to realize the desired/required optical properties/characteristics.Appropriate materials that may be deposited on the second structurallayer 38 for providing the desired/required optical properties includegold, silver, and aluminum for metal coatings. For metals, gold and anassociated adhesion layer are preferable to obtain a suitablereflectance.

[0078] Depending upon the method of manufacture, a plurality of smalletch release holes (not shown) may be formed through the entire verticalextent of the first and/or second structural layer 34, 38 to allow forthe removal of any sacrificial layer(s) that is disposed between thefirst structural layer 34 and the second structural layer 38 of themirror microstructure 30, and that is disposed between the firststructural layer 34 and the substrate 54, respectively, when the mirrormicrostructure 30 is released from the substrate 54 (i.e., during thefabrication of the mirror microstructure 30). For instance, using thegeneral principles of the manufacturing technique represented in FIGS.12A-M to define the microstructure 30 would require such etch releaseholes. It should be appreciated that having etch release holes thatextend entirely through the second structural layer 38, and which arethereby exposed on its upper surface 46, may have an adverse effect onits optical performance capabilities. Certain degradations in opticalperformance may be acceptable in some instances. However, the mirrormicrostructure 30 also may be made without having any etch release holesthat extend down through the second structural layer 38, including inaccordance with the methodology represented in FIGS. 17A-G.

[0079] Various desirable characteristics of the types of reinforcedmirror microstructures described herein are addressed following thediscussion of various other embodiments. Certain parameters are used inthis summarization. One such parameter is the diameter of the uppermoststructural layer in the mirror microstructure, and that is representedby the dimension “d_(SL)” (“SL” being an acronym for “structurallayer”). “Diameter” does not of course limit this uppermost structurallayer to having a circular configuration (in plan view), but is a simplythe distance of a straight cord or line that extends laterally from onelocation on a perimeter of this uppermost structural layer, through acenter of this uppermost structural layer, and to another location onthe perimeter of this uppermost structural layer. The dimension d_(SL)for the case of the mirror microstructure 30 thereby represents thediameter of the second structural layer 38 (the distance from onelocation on a perimeter 44 of the second structural layer 38, through acenter 42 of the second structural layer 38, and to another location onthis perimeter 44).

[0080] Another parameter that is used in the summarization of thedesirable characteristics of the mirror microstructures disclosed hereinis the distance from the center (in the lateral dimension) of theuppermost structural layer in the mirror microstructure to thatreinforcing structure (by engaging a lower surface of this uppermoststructural layer) which is closest to the center of this uppermoststructural layer. This is represented by the dimension “d_(RS)” (“RS”being an acronym for “reinforcing structure”). The dimension d_(RS) forthe case of the mirror microstructure 30 represents the distance fromthe center 42 of the second structural layer 38 to that column 50 whichis closest to the center 42. A final parameter that is used in the notedsummarization is the radius of curvature of the uppermost structurallayer in the mirror microstructure (i.e., the amount which thisuppermost structural layer is “cupped” or “bulged”). This is representedby the dimension RC. The dimension RC for the case of the mirrormicrostructure 30 thereby defines the radius of curvature of the secondstructural layer 38.

[0081] Another configuration of a mirror microstructure for a surfacemicromachined optical system, such as for the mirror microstructures 6and 20 in the surface micromachined optical systems 2 and 16 of FIGS. 1Aand 1B-C, respectively, is presented in FIG. 4 in the form of athree-layered mirror microstructure 58. The mirror microstructure 58 isfabricated on a substrate 60 by surface micromachining techniques.Components of the mirror microstructure include a first structural layeror support 62 that is spaced vertically upward relative to the substrate60 (e.g., disposed at a higher elevation than the substrate 60), asecond structural layer or support 78 that is spaced vertically upwardrelative to the first structural layer 62 (e.g., disposed at a higherelevation relative to the substrate 60), a third structural layer orsupport 94 that is spaced vertically upward relative to the secondstructural layer 78 (e.g., disposed at a higher elevation relative tothe substrate 60), a plurality of separate and discrete first columns orposts 74 that are disposed in spaced relation to each other, and aplurality of separate and discrete second columns or posts 90 that arealso disposed in spaced relation to each other. The first columns 74extend between and fixedly interconnect the first structural layer 62and the second structural layer 78, while the second columns 90 extendbetween and fixedly interconnect the second structural layer 78 and thethird structural layer 94, all for structurally reinforcing the mirrormicrostructure 58 and, more particularly, the third structural layer 94.Therefore, the first structural layer 62, the second structural layer78, the interconnecting columns 74, the third structural layer 94, andthe interconnecting columns 90 may be moved simultaneously if acted uponby any interconnected actuator to provide a desired/required opticalfunction.

[0082] The first columns 74 may be disposed in either equally spacedrelation or the spacing between adjacent columns 74 may vary in at leastsome manner. The same applies to the columns 90. The plurality of firstcolumns 74 may be offset in relation to the plurality of second columns90 or such that no first column 74 is axially aligned (in the verticaldirection) with any second column 90 as shown. However, other relativepositionings between the plurality of first columns 74 and plurality ofsecond columns 90 may be utilized as well, including where one or moreof the plurality of first columns 74 is at least partially aligned witha second column 90.

[0083] An upper surface 102 of the third structural layer 94 is orincludes an optically reflective layer or film. That is, the materialsthat are used to define the third structural layer 94 may provide thedesired/required optical properties/characteristics for the mirrormicrostructure 58. More typically a separate layer or film will bedeposited on the third structural layer 94 to realize thedesired/required optical properties/characteristics. Those materialsdiscussed above in relation to the mirror microstructure 30 for thispurpose may be utilized by the mirror microstructure 58 and in thegeneral manner illustrated in FIG. 2B.

[0084] Depending upon the method of fabrication, a plurality of smallrelease holes (not shown) may be formed through the entire verticalextent of one or more of the first structural layer 62, the secondstructural layer 78, and the third structural layer 94 to allow for theremoval of any underlying and adjacently disposed sacrificial layer(s),or when the mirror microstructure 58 is released from the substrate 60(i.e., during the fabrication of the mirror microstructure 58). Forinstance, using the general principles of the manufacturing techniquerepresented in FIGS. 12A-M to define the mirror microstructure 58 wouldrequire such etch release holes. It should be appreciated that havingetch release holes that extend entirely through the third structurallayer 94, and which are thereby exposed on its upper surface 102, mayhave an effect on its optical performance capabilities. Certaindegradations in optical performance may be acceptable in some instances.However, the mirror microstructure 58 also may be made without havingany etch release holes that extend down through the third structurallayer 94, including in accordance with the methodology represented inFIGS. 17A-G.

[0085] Certain parameters are identified on FIG. 4 and that areaddressed in the above-noted summarization of certain desirablecharacteristics that follows below. The dimension “d_(SL)” for the caseof the mirror microstructure 58 represents the diameter of the thirdstructural layer 94 (e.g., a line that extends laterally from onelocation on a perimeter 70 of the third structural layer 94, through acenter 66 of the third structural layer 94, and to another location onthis perimeter 70) that is being structurally reinforced collectively bythe plurality of columns 90, the second structural layer 78, theplurality of columns 74, and the first structural layer 62. Thedimension “d_(RS)” for the case of the mirror microstructure 58represents the distance from the center 66 of the third structural layer94 to that column 90 which is closest to the center 66. Finally, RC forthe case of the mirror microstructure 58 represents the radius ofcurvature of the third structural layer 94.

[0086] Another configuration of a mirror microstructure for a surfacemicromachined optical system, such as for the mirror microstructures 6and 20 in the surface micromachined optical systems 2 and 16 of FIGS. 1Aand 1B-C, respectively, is presented in FIGS. 5-6 in the form of atwo-layered mirror microstructure 106. The mirror microstructure 106 isfabricated on a substrate 108 by surface micromachining techniques.Components of the mirror microstructure 106 include a first structurallayer or support 110 that is spaced vertically upward relative to thesubstrate 108 (e.g., disposed at a higher elevation relative to thesubstrate 108), a second structural layer or support 122 that is spacedvertically upward relative to the first structural layer 110 (e.g.,disposed at a higher elevation relative to the substrate 108), and aplurality of at least generally laterally extending ribs or rails 118(i.e., with their length dimension being measured in a lateral dimensionor at least generally parallel with the substrate 108). The upper andlower extremes of the rails 118 extend between and fixedly interconnectthe first structural layer 110 and the second structural layer 122 tostructurally reinforce the mirror microstructure 106 and, moreparticularly, the second structural layer 122. Therefore, the secondstructural layer 122 and first structural layer 110, along with theinterconnecting rails 118, may be moved simultaneously if acted upon byany interconnected actuator to provide a desired/required opticalfunction.

[0087] The rails 118 further extend at least generally laterally fromone location on or at least generally proximate to a perimeter 116 ofthe microstructure 106 (e.g., within 50 μm of the perimeter 116, morepreferably within 25 μm of this perimeter 116) to another location on orat least generally proximate to this perimeter 116 (e.g., within 50 μmof the perimeter 116, more preferably within 25 μm of this perimeter116). In the illustrated embodiment, the rails 118 are of an axial orlinear configuration in the lateral dimension, and further are disposedin at least generally parallel and equally spaced relation.

[0088] An upper surface 126 of the second structural layer 122 is orincludes an optically reflective layer or film. That is, the materialsthat are used to define the second structural layer 126 may provide thedesired/required optical properties/characteristics for the mirrormicrostructure 106. More typically a separate layer or film will bedeposited on the second structural layer 122 to realize thedesired/required optical properties/characteristics. Those materialsdiscussed above in relation to the mirror microstructure 30 for thispurpose may be utilized by the mirror microstructure 106 and in thegeneral manner illustrated in FIG. 2B.

[0089] There are a number of significant advantages in relation to thedesign utilized by the mirror microstructure 106 of FIGS. 5-6. First isin relation to its optical characteristics. The upper surface 126 of thesecond structural layer 122 of the mirror microstructure 106 need notand preferably does not include any vertically disposed etch releaseholes which extend downwardly therethrough in order to allow for theremoval of any sacrificial material from between the first structurallayer 110 and the second structural layer 122 when the microstructure106 is released from the substrate 108, which significantly enhances theoptical performance capabilities of the mirror microstructure 106(vertically disposed etch release holes would extend through the firststructural layer 110 to remove any sacrificial material between thefirst structural layer 110 and the substrate 108). That is, preferablythe upper surface 126 of the mirror microstructure 106 is continuous anddevoid of any indentations, etch release holes, or the like (depressionsor indentations that may develop on the upper surface 126 of the secondstructural layer 122 from the manufacture of the mirror microstructure106 may be addressed by a planarization operation). Exactly how themirror microstructure 106 may alleviate the need for the etch releaseholes in the second structural layer 122 will be discussed in moredetail below in relation to the manufacturing methodologies representedin FIGS. 12A-M, 13A-M, 15A-G, and 17A-G. Suffice it to say for presentpurposes that the rails 118 may at least assist in the definition of aplurality of at least generally laterally extending etch release pipes,channels, or conduits in a sacrificial layer(s) that is disposed betweenthe second structural layer 122 and the first structural layer 110during the manufacture of the mirror microstructure 106. Any railsdescribed herein that provide this function are characterized as etchrelease rails or the like. How the rails 118 are oriented relative toeach other, or stated another way the layout of the rails 118, may havean effect on their ability to create this plurality of etch releasechannels or conduits within any sacrificial layer that is disposedbetween the first structural layer 110 and the second structural layer122 during the manufacture of the mirror microstructure 106 by surfacemicromachining techniques. The general design considerations for etchrelease rails is summarized below following the description of otherembodiments of microstructures that include etch release rails.

[0090] Another function provided by the plurality of rails 118 isstructural reinforcement of the second structural layer 122. That is,the plurality of rails 118 structurally interconnect the secondstructural layer 122 with the first structural layer 110. The structuralreinforcement function of the rails 118 would not be adversely affected,and may in fact improve, by having at least some of the rails 118 bedisposed in intersecting relation (e.g., see FIGS. 9A-B).

[0091] Certain parameters are identified on one or more of FIGS. 5-6 andthat are addressed in the above-noted summarization of desirablecharacteristics that follows below. The dimension “d_(SL)” for the caseof the mirror microstructure 106 represents the diameter of the secondstructural layer 122 (e.g., the distance of a line that extends from onelocation on the perimeter 116 of the second structural layer 122,through a center 114 of the second structural layer 122, and to anotherlocation on this perimeter) that is being structurally reinforcedcollectively by the plurality of rails 118 and the first structurallayer 110. The dimension “d_(RS)” for the case of the mirrormicrostructure 106 represents the distance from the center 114 of thesecond structural layer 122 to that rail 118 that is closest to thecenter 114, which is “0” in the illustrated embodiment (FIG. 6) sinceone of the rails 118 actually extends through the center 114. It shouldbe appreciated that a rail 118 need not extend through the center 114,in which case d_(RS) would have a value greater than “0.” Finally, RCfor the case of the mirror microstructure 106 represents the radius ofcurvature of the second structural layer 122.

[0092] Another configuration of a mirror microstructure for a surfacemicromachined optical system, such as for the mirror microstructures 6and 20 in the surface micromachined optical systems 2 and 16 of FIGS. 1Aand 1B-C, respectively, is presented in FIGS. 6-8 in the form of athree-layered mirror microstructure 130. The mirror microstructure 130is fabricated on an appropriate substrate 132 by surface micromachiningtechniques. Components of the mirror microstructure 130 include a firststructural layer or support 134 that is spaced vertically upwardrelative to the substrate 132 (e.g., disposed at a higher elevation thanthe substrate 132), a second structural layer or support 146 that isspaced vertically upward relative to the first structural layer 134(e.g., disposed at a higher elevation relative to the substrate 132), athird structural layer or support 158 that is spaced vertically upwardrelative to the second structural layer 146 (e.g., disposed at a higherelevation relative to the substrate 132), a plurality of at leastgenerally laterally extending first rails 142, and a plurality of atleast generally laterally extending second rails 154. The first rails142 extend between and fixedly interconnect the first structural layer134 and the second structural layer 146, while the second rails 154extend between and fixedly interconnect the second structural layer 146and the third structural layer 158, all to structurally reinforce themirror microstructure 130 and, more particularly, the third structurallayer 158. Therefore, the first structural layer 134, the secondstructural layer 146, the interconnecting rails 142, the thirdstructural layer 158, and the interconnecting rails 154 may be movedsimultaneously if acted upon by any interconnected actuator to provide adesired/required optical function.

[0093] The rails 154 extend at least generally laterally from onelocation on or at least generally proximate to a perimeter 138 of thethird structural layer 158 (e.g., within 50 μm of the perimeter 138,more preferably within 25 μm of this perimeter 138) to another locationon or least generally proximate to this perimeter 138 (e.g., within 50μm of the perimeter 138, more preferably within 25 μm of this perimeter138). In the illustrated embodiment, the plurality of rails 154 are ofan axial or linear configuration in the lateral dimension, and furtherare disposed in at least generally parallel and equally spaced relation.The plurality of rails 142 are also of an axial or linear configurationin the lateral dimension, and further are disposed in at least generallyparallel and equally spaced relation.

[0094] An upper surface 162 of the third structural layer 158 is orincludes an optically reflective layer or film. That is, the materialsthat are used to define the third structural layer 158 may provide thedesired/required optical properties/characteristics for the mirrormicrostructure 130. More typically a separate layer or film will bedeposited on the third structural layer 158 to realize thedesired/required optical properties/characteristics. Those materialsdiscussed above in relation to the mirror microstructure 30 for thispurpose may be utilized by the mirror microstructure 130 and in thegeneral manner illustrated in FIG. 2B.

[0095] There are a number of significant advantages in relation to thedesign utilized by the mirror microstructure 130. First is in relationto its optical characteristics. The upper surface 162 of the thirdsupport layer 158 of the mirror microstructure 130 need not andpreferably does not include any vertically disposed etch release holesin order to allow for the removal of any sacrificial material frombetween the third structural layer 158 and the second structural layer146 when the microstructure 130 is released from the substrate 132,which significantly enhances the optical capabilities of the mirrormicrostructure 130. That is, preferably the upper surface 162 of themirror microstructure 130 is continuous and devoid of any indentations,holes, or the like (depressions or indentations that may develop on theupper surface 162 of the third support layer 158 during the manufacturethe microstructure 130 may be addressed by a planarization operation).Exactly how the mirror microstructure 130 may alleviate the need for anyvertically disposed etch release holes in the third structural layer 158will be discussed in more detail below in relation to the manufacturingmethodologies represented in FIGS. 12A-M, 13A-M, 15A-G, and 17A-G.Suffice it to say for present purposes that the rails 154 may at leastassist in the definition of a plurality of laterally extending etchrelease pipes, channels, or conduits in a sacrificial layer(s) that isdisposed between the second structural layer 146 and the thirdstructural layer 158 during the manufacture of the mirror microstructure130. As such, the rails 154 may be characterized as etch release railsas noted above. Again and in this case, how the rails 154 are orientedrelative to each other, or stated another way the layout of the rails154, may have an effect on their ability to create this plurality ofetch release channels or conduits within any sacrificial layer that isdisposed between the second structural layer 146 and the thirdstructural layer 158 during the manufacture of the mirror microstructure130 by surface micromachining techniques. The general designconsiderations for etch release rails again are summarized belowfollowing the description of the various embodiments of microstructuresthat include such etch release rails.

[0096] In the event that it would be desirable to avoid the use of etchrelease holes in the second structural layer 146 to allow for theremoval of any sacrificial layer(s) that is disposed between the secondstructural layer 146 and the first structural layer 134, thecharacteristics noted above in relation to the rails 154 could beutilized by the rails 142 as well. Etch release holes would likely berequired in the first structural layer 134 in order to allow for theremoval of any sacrificial layer(s) that is disposed between the firststructural layer 134 and the substrate 132 during the release of themicrostructure 130 from the substrate 132.

[0097] Another function provided by the plurality of first rails 142 andsecond rails 154 is structural reinforcement of the mirrormicrostructure 130, and more particularly the third structural layer158. It is believed that enhanced structural reinforcement is realizedby having the plurality of first rails 142 disposed in a differentorientation within the lateral dimension than the plurality of secondrails 154. In the illustrated embodiment, the plurality of first rails142 are disposed at least substantially perpendicular to the pluralityof second rails 154 in the lateral dimension. The structuralreinforcement function of the rails 142 and 154 would not be adverselyaffected, and may fact improve, by having at least some of the rails 142be disposed in intersecting in relation and/or by having at least someof the rails 154 be disposed in intersecting relation (e.g., see FIGS.9A-B).

[0098] Certain parameters are identified on one or more of FIGS. 6-8 inrelation to the mirror microstructure 130 and that are addressed in theabove-noted summarization of desirable characteristics that followsbelow. The dimension “d_(SL)” for the case of the microstructure 130represents the diameter of the third structural layer 158 (e.g., thedistance of a straight line that extends from one location on theperimeter 138 of the third structural layer 158, through a center 136 ofthe third structural layer 158, and to another location on thisperimeter 138) that is being structurally reinforced collectively by theplurality of rails 154, the second structural layer 146, the pluralityof rails 142, and the first structural layer 134. The dimension “d_(RS)”for the case of the microstructure 130 represents the distance from thecenter 136 of the third structural layer 158 to that rail 154 that isclosest to the center 136, which is “0” in the illustrated embodimentsince one of the rails 154 actually extends through the center 136. Itshould be appreciated that a rail 154 need not extend through the center136, in which case d_(RS) would have a value greater than “0.” Finally,RC for the case of the mirror microstructure 130 represents the radiusof curvature of the third structural layer 158.

[0099] Another configuration of a mirror microstructure for a surfacemicromachined optical system, such as for the mirror microstructures 6and 20 in the surface micromachined optical systems 2 and 16 of FIGS. 1Aand 1B-C, respectively, is presented in FIGS. 9A-B in the form of atwo-layered mirror microstructure 166. The mirror microstructure 166 isfabricated on a substrate 168 by surface micromachining techniques.Components of the mirror microstructure 166 include a first structurallayer or support 170 that is spaced vertically upward relative to thesubstrate 168 (e.g., disposed at a higher elevation relative to thesubstrate 168), a second structural layer or support 172 that is spacedvertically upward relative to the first structural layer 170 (e.g.,disposed at a higher elevation relative to the substrate 168), aplurality of at least generally laterally extending first rails 174 thatare disposed in spaced relation, and a plurality of at least generallylaterally extending second rails 178 that are also disposed in spacedrelation. Both the first rails 174 and the second rails 178 extendbetween and fixedly interconnect the first structural layer 170 and thesecond structural layer 172 to structurally reinforce the microstructure166 and, more particularly, the second structural layer 172. In theillustrated embodiment, the plurality of first rails 174 are disposed inat least substantially parallel and equally spaced relation, as are theplurality of second rails 178. However, the plurality of first rails 174are not disposed in the same orientation as the plurality of secondrails 178 in the lateral dimension. In the illustrated embodiment, thefirst rails 174 are disposed at least substantially perpendicular to thesecond rails 178. As such, the first structural layer 170 and secondstructural layer 172, as well as the interconnecting rails 174, 178, maybe moved simultaneously if acted upon by any interconnected actuator toprovide a desired/required optical function.

[0100] The plurality of first rails 174 and the plurality of secondrails 178 will not form the type of etch release channels or conduits inany sacrificial layer that may exist between the first structural layer170 and the second structural layer 172 during the manufacture of themirror microstructure 166 using surface micromachining in comparison tothe mirror microstructures 106 and 130 discussed above. As such, aplurality of small vertically disposed etch release holes (not shown)will typically extend through the entire vertical extent of the secondstructural layer 172 to allow for the removal of any sacrificiallayer(s) that is disposed between the first structural layer 170 and thesecond structural layer 172 of the mirror microstructure 166 used in theassembly thereof (a plurality of small vertically disposed etch releaseholes (not shown) will also typically extend through the entire verticalextent of the first structural layer 170 to allow for the removal of anysacrificial layer(s) that is disposed between the first structural layer170 and the substrate 168 of the mirror microstructure 166 to releasethe microstructure 166 from the substrate 168). This again may have anadverse impact on the optical performance capabilities of an uppersurface 176 of the second structural layer 172. However, themicrostructure 166 still has desirable structural reinforcementcharacteristics. In this regard, the plurality of first rails 174 andthe plurality of second rails 178 may be viewed as defining a grid 177having a plurality of closed cells 179 (i.e., having a closed boundary).Any appropriate configuration may be used to define the perimeter ofthese closed cells 179 (e.g., a honeycomb, cylindrical), and each suchclosed cell 179 need not be of the same configuration.

[0101] An upper surface 176 of the second structural layer 172 is orincludes an optically reflective layer or film of the type discussedabove in relation to the mirror microstructure 30. Due to the likelyexistence of the plurality of vertically disposed etch release holes inthe second structural layer 172, the upper surface 176 will at leasthave a plurality of dimples or the like which may have an effect on itsoptical performance capabilities. As such, the principal advantage ofthe mirror microstructure 166 is the structural reinforcement of thesecond structural layer 172 that is provided by the plurality of rails174, 178 that structurally interconnect the second structural layer 172with the first structural layer 170.

[0102] Certain parameters are identified on one or more of FIGS. 9A-Band that are addressed in the above-noted summarization of desirablecharacteristics that follows below. The dimension “d_(SL)” for the caseof the microstructure 166 represents the diameter of the secondstructural layer 172 (e.g., the distance of a straight line that extendsfrom one location on a perimeter 173 of the second structural layer 172,through a center 171 of the second structural layer 172, and to anotherlocation on this perimeter 173) that is being structurally reinforcedcollectively by the plurality of rails 174, the rails, 178, and thefirst structural layer 170. The dimension “d_(RS)” for the case of themicrostructure 166 represents the distance from the center 171 of thesecond structural layer 172 to that portion of the grid 177 that isclosest to the center 171. Finally, RC for the case of themicrostructure 166 represents the radius of curvature of the secondstructural layer 172.

[0103] Another configuration of a mirror microstructure for a surfacemicromachined optical system, such as for the mirror microstructures 6and 20 in the surface micromachined optical systems 2 and 16 of FIGS. 1Aand 1B-C, respectively, is presented in FIGS. 10A-C in the form of areinforced, single-layer mirror microstructure 384. The mirrormicrostructure 384 is fabricated on a substrate 386 by surfacemicromachining techniques and is separated therefrom by a space 392.Other structural components could be disposed within this space 392,although any such structures would typically be spaced from the mirrormicrostructure 384 at least when providing its optical function.Components of the mirror microstructure 384 include a structural layeror support 404 that is spaced vertically upward relative to thesubstrate 386 (e.g., disposed at a higher elevation relative to thesubstrate 386); a plurality of at least generally laterally extendingrails 400 that are fixedly interconnected with the structural layer 404,that extend toward but not to the substrate 386, and that are disposedin a first orientation; and a plurality of at least generally laterallyextending rails 396 that are fixedly interconnected with the lowerextreme of the rails 400 at a plurality of discrete locations, thatextend toward but not to the substrate 386, and that are disposed in asecond orientation that is different than the first orientation. In theillustrated embodiment, the rails 400 are disposed at least generallyperpendicular to the rails 396, although other relative orientations orrelative angular positions could be utilized. Therefore, the structurallayer 404, as well as the rails 400 and 396, may be moved simultaneouslyif acted upon by any interconnected actuator to provide adesired/required optical function.

[0104] At least the rails 400, and possibly the rails 396, extend atleast generally laterally from one radial location corresponding with orat least generally proximate to a perimeter 390 of the microstructure384 (e.g., within 50 μm of the perimeter 390, more preferably within 25μm of this perimeter 390) to another radial location corresponding withor at least generally proximate to this perimeter 390 (e.g., within 50μm of the perimeter 390, more preferably within 25 μm of this perimeter390). In the illustrated embodiment, the rails 400 are of an axial orlinear configuration in the lateral dimension, and are further disposedin at least generally parallel and equally spaced relation, while therails 396 are also of an axial or linear configuration in the lateraldimension, and are further disposed in at least generally parallel andequally spaced relation.

[0105] An upper surface 406 of the structural layer 404 is or includesan optically reflective layer or film. That is, the materials that areused to define the structural layer 404 may provide the desired/requiredoptical properties/characteristics for the mirror microstructure 384.More typically a separate layer or film will be deposited on thestructural layer 404 to realize the desired/required opticalproperties/characteristics. Those materials discussed above in relationto the mirror microstructure 30 for this purpose may be utilized by themirror microstructure 384 and in the general manner illustrated in FIG.2B.

[0106] There are a number of significant advantages in relation to thedesign utilized by the mirror microstructure 384. First is in relationto its optical characteristics. The upper surface 406 of the supportlayer 404 of the mirror microstructure 384 need not and preferably doesnot include any vertically disposed etch release holes which extendentirely through the structural layer 404 in order to allow for theremoval of any sacrificial material from between the structural layer404 and the substrate 386 when the microstructure 384 is released fromthe substrate 386, which significantly enhances the optical performancecapabilities of the mirror microstructure 384. That is, preferably theupper surface 406 of the mirror microstructure 384 is continuous anddevoid of any indentations, etch release holes, or the like (depressionsor indentations that may develop on the upper surface 406 of thestructural layer 404 from the manufacture of the mirror microstructure384 may be addressed by a planarization operation). Exactly how themirror microstructure 384 may alleviate the need for the etch releaseholes in the structural layer 404 will be discussed in more detail belowin relation to the manufacturing methodologies represented in FIGS.12A-M, 13A-M, 15A-G, and 17A-G. Suffice it to say for present purposesthat the rails 396, the rails 400, or both may at least assist in thedefinition of a plurality of at least generally extending etch releasepipes, channels, or conduits in a sacrificial layer(s) to allow for amore expedient removal of the same and without the need for anyconventional etch release holes that extend downwardly entirely throughthe structural layer 404. As such, the plurality of rails 396 and 404may both be characterized as etch release rails as noted above. Againand in this case, how the rails 400 are oriented relative to each otherand how the rails 396 are oriented relative to each other, or statedanother way the layout of the rails 396 and 404, may have an effect ontheir respective abilities to these etch release conduits within anysacrificial layer that is disposed between the structural layer 404 andthe substrate 386 during the manufacture of the mirror microstructure384 by surface micromachining techniques. The general designconsiderations for etch release rails again are summarized belowfollowing the description of the various embodiments of microstructuresthat include such etch release rails.

[0107] Another function provided by the plurality of rails 400 and theplurality of rails 396 is structural reinforcement of the microstructure384 and, more particularly the structural layer 404. In the illustratedembodiment, the rails 400 provide enhanced stiffness in effectively onedirection and the plurality of rails 396 provide enhanced stiffness ineffectively one direction as well, but different from that associatedwith the rails 400. It is believed that enhanced structuralreinforcement is realized by having the plurality of rails 400 disposedin a different orientation within the lateral dimension than theplurality of rails 396. In the illustrated embodiment, the plurality ofrails 400 are disposed at least substantially perpendicular to theplurality of rails 396 in the lateral dimension. The structuralreinforcement function of the rails 400 and 396 would not be adverselyaffected, and may in fact improve, by having at least some of the rails400 be disposed in intersecting in relation and/or by having at leastsome of the rails 396 be disposed in intersecting relation (e.g., seeFIGS. 9A-B).

[0108] Certain parameters are identified on one or more of FIGS. 10A-Cin relation to the mirror microstructure 384 and that are addressed inthe above-noted summarization of the desirable characteristics thatfollows below. The dimension “d_(SL)” for the case of the microstructure384 represents the diameter of the structural layer 404 (e.g., thedistance of a straight line that extends from one location on theperimeter 390 of the structural layer 404, through a center 388 of thestructural layer 404, and to another location on this perimeter 390)that is being structurally reinforced collectively by the plurality ofrails 400 and the plurality of rails 396. The dimension “d_(RS)” for thecase of the microstructure 384 represents the distance from the center388 of the structural layer 404 to that rail 400 that is closest to thecenter 388. Finally, RC for the case of the mirror microstructure 384represents the radius of curvature of the structural layer 404.

[0109]FIG. 10D presents a variation of the mirror microstructure 384 ofFIGS. 10A-C. The only difference between the FIGS. 10A-C and FIG. 10Dconfigurations is that the rails 400 in the FIGS. 10A-C configurationare replaced with a plurality of columns or posts 400′ in the FIG. 10Dconfiguration. The FIG. 10D configuration still provides at least somedegree of structural reinforcement for the structural layer 404, andalso allows for formation of etch release conduits along the length ofthe rails 396.

[0110] Other layouts of rails that provide/allow for the formation ofthe etch release conduits in a sacrificial layer(s) (i.e., etch releaserails), are within the scope of the present invention. Representativeexamples of other etch release rail layouts that may be appropriate forforming etch release channels and that may be used in any of theabove-described embodiments of mirror microstructures are presented inFIGS. 11A-F. FIG. 11A illustrates an embodiment in which a plurality ofrails 412 are fixed to and extend away from a structural layer orsupport 408. These rails 412 may “cantilever” from this structural layer408, or alternatively may interconnect the structural layer 408 withanother structural layer (not shown) to provide a multi-layered mirrormicrostructure. In any case, the rails 412 have what may becharacterized as a sinusoidal lateral dimension or a sinusoidalconfiguration in plan view, and further extend from one location on orat least generally proximate to a perimeter 410 (e.g., within 50 μm ofthis perimeter 410, more preferably within 25 μm of this perimeter 410)of the structural layer 408 to another location on or at least generallyproximate to this perimeter (e.g., within 50 μm of this perimeter 410,more preferably within 25 μm of this perimeter 410). Stated another way,the plurality of rails 412 extend sinusoidally within a plane that is atleast generally parallel with the substrate 408. In the illustratedembodiment, none of the rails 412 intersect and adjacent rails 412 arenested to a degree such that the peaks 416 of one rail 412 extend atleast partially within the space defined by a corresponding trough 420of the adjacent rail 412. Stated another way, the peaks 416 of one rail412 preferably extend beyond a line that is tangent to the troughs 420of an adjacent rail 412. The “amplitude” of this sinusoidalconfiguration need not remain constant along the length of the rails412. The rails 412 also may be characterized as “meandering” so as toprovide enhanced stiffness in more than one dimension. Other“meandering” configurations than the sinusoidal type illustrated inrelation to FIG. 11A may be utilized as well for structuralreinforcement and to allow for the formation of etch release channels(e.g., in zig-zag fashion).

[0111]FIG. 11B illustrates an embodiment in which a plurality of rails436 are fixed to and extend away from a structural layer or support 424.These rails 436 may “cantilever” from this structural layer 424, oralternatively may interconnect the structural layer 424 with anotherstructural layer (not shown) to provide a multi-layered mirrormicrostructure. In any case, instead of being disposed in parallelrelation, the plurality of rails 436 are at least generally radiallydisposed or extending (but still within the lateral dimension). In theillustrated embodiment, the plurality of rails 436 extend from or atleast generally proximate to a perimeter 428 (e.g., within 50 μm of thisperimeter 428, more preferably within 25 μm of this perimeter 428) ofthe structural layer 424 toward, but not to, a center 432 of thestructural layer 424.

[0112]FIG. 11C illustrates an embodiment in which a plurality of rails452, 456 are fixed to and extend away from a structural layer or support440. These rails 452, 456 may “cantilever” from this structural layer440, or alternatively may interconnect the structural layer 440 withanother structural layer (not shown) to provide a multi-layered mirrormicrostructure. In any case, instead of being disposed in parallelrelation, the plurality of rails 452, 456 are at least generallyradially disposed or extending (but still within the lateral dimension).In the illustrated embodiment, the plurality of rails 452, 456 extendfrom or at least generally proximate to a perimeter 444 (e.g., within 50μm of this perimeter 444, more preferably within 25 μm of this perimeter444) of the structural layer 440 at least toward a center 448 of thestructural layer 440. The rails 452 extend further toward the center 448than the rails 456. This reduces the potential for adversely affectingthe formation of the etch release channels at radially inward locations(i.e., at locations that are closer to the center 448).

[0113]FIG. 11D illustrates an embodiment in which a plurality of firstrails 508 and a plurality of second rails 512 are fixed to and extendaway from a structural layer or support 500. These rails 508, 512 may“cantilever” from this structural layer 500, or alternatively mayinterconnect the structural layer 500 with another structural layer (notshown) to provide a multi-layered mirror microstructure. In any case,instead of being disposed in parallel relation, the plurality of firstrails 508 and the plurality of second rails 512 are at least generallyradially disposed or extending (but still within the lateral dimension).In the illustrated embodiment, the plurality of first rails 508 and theplurality of second rails 512 extend from or at least generallyproximate to a perimeter 504 (e.g., within 50 μm of this perimeter 504,more preferably within 25 μm of this perimeter 504) of the structurallayer 500 toward, but not to, a center 506 of the structural layer 500.Generally, the plurality of first rails 508 extend further toward thecenter 506 than do the plurality of second rails 512, and at least onesecond rail 512 is disposed between adjacent pairs of first rails 508.

[0114]FIG. 11E illustrates an embodiment in which a plurality of firstrails 528, second rails 532, third rails 540, and fourth rails 548 arefixed to and extend away from a structural layer or support 516.Although these rails 528, 532, 540, and 548 are illustrated as beingsimply a line in FIG. 11E, it should be appreciated that these rails528, 532, 540, and 548 may be of any appropriate width. These rails 528,532, 540, and 548 may “cantilever” from this structural layer 516, oralternatively may interconnect the structural layer 516 with anotherstructural layer (not shown) to provide a multi-layered mirrormicrostructure. In the illustrated embodiment, all of the rails 528,532, 540, and 548 are not disposed in parallel relation to each other,and furthermore all of the rails 528, 532, 540, and 548 are not radiallydisposed or extending within the lateral dimension (i.e., all rails 528,532, 540, and 548 do not extend toward a point corresponding with acenter 524 of the structural layer 516). Instead, in the illustratedembodiment: 1) the plurality of first rails 528 extend from or at leastgenerally proximate to a perimeter 520 (e.g., within 50 μm of thisperimeter 520, more preferably within 25 μm of this perimeter 520) ofthe structural layer 516 to a point corresponding with the center 524 ofthe structural layer 516—that is, the rails 528 intersect at a pointcorresponding with the center 524, and effectively define a column orpost that is disposed at the center 524; 2) a pair of second rails 532are disposed between each adjacent pair of first rails 528, and extendfrom or at least generally proximate to the perimeter 520 (e.g., within50 μm of this perimeter 520, more preferably within 25 μm of thisperimeter 520) of the structural layer 516 to an intersection 536 thatis, a pair of second rails 532 that terminate at an intersection 536 are“nested” between each adjacent pair of first rails 528; 3) a pair ofthird rails 540 are disposed within the space that is inward of eachpair of second rails 532 that are joined at an intersection 536, andextend from or at least generally proximate to the perimeter 520 (e.g.,within 50 μm of this perimeter 520, more preferably within 25 μm of thisperimeter 520) of the structural layer 516 to an intersection 544 thatis, a pair of third rails 540 that terminate at an intersection 544 are“nested” between each adjacent pair of second rails 532 that are joinedat an intersection 536; and 4) a pair of fourth rails 548 are disposedwithin the space that is inward of each pair of third rails 540 that arejoined at an intersection 544, and extend from or at least generallyproximate to the perimeter 520 (e.g., within 50 μm of this perimeter520, more preferably within 25 μm of this perimeter 520) of thestructural layer 516 to an intersection 552—that is, a pair of fourthrails 548 that terminate at an intersection 552 are “nested” betweeneach adjacent pair of third rails 540 that are joined at an intersection544. Therefore, the layout presented in FIG. 11E has at least some etchrelease rails that intersect at one common point (e.g., rails 528 thatintersect at a point corresponding with the center 524), while otherrails intersect at a different common point (e.g., at intersections 536,544, 552).

[0115]FIG. 11F illustrates an embodiment in which a plurality of firstrails 568, second rails 572, third rails 576, and fourth rails 580 arefixed to and extend away from a structural layer or support 556. Theserails 568, 572, 576, and 580 may “cantilever” from this structural layer556, or alternatively may interconnect the structural layer 556 withanother structural layer (not shown) to provide a multi-layered mirrormicrostructure. In any case, instead of being disposed in parallelrelation, the plurality of rails 568, 572, 576, and 580 are at leastgenerally radially disposed or extending (but still within the lateraldimension). That is, the plurality of rails 568, 572, 576, and 580extend from or at least generally proximate to a perimeter 560 (e.g.,within 50 μm of this perimeter 560, more preferably within 25 μm of thisperimeter 560) of the structural layer 556 at least toward a pointcorresponding with a center 564 of the structural layer 556. Generally,the rails 568, 572, 576, and 580 terminate at different radial positionsrelative to the center 564 of the structural layer 556. In theillustrated embodiment: 1) the plurality of first rails 568 extend fromor at least generally proximate to the perimeter 560 (e.g., within 50 μmof this perimeter 560, more preferably within 25 μm of this perimeter560) of the structural layer 556 to the center 564 of the structurallayer 556—that is, the plurality of first rails 568 intersect at acommon point corresponding with the center 564, and effectively define acolumn or post that is disposed at the center 564; 2) one second rail572 is disposed between each adjacent pair of first rails 568, andextends from or at least generally proximate to the perimeter 560 (e.g.,within 50 μm of this perimeter 560, more preferably within 25 μm of thisperimeter 560) of the structural layer 556 toward, but not to, thecenter 564 of the structural layer 556; 3) one third rail 576 isdisposed between each first rail 568 and an adjacent second rail 572,and extends from or at least generally proximate to the perimeter 560(e.g., within 50 μm of this perimeter 560, more preferably within 25 μmof this perimeter 560) of the structural layer 556 toward, but not to,the center 564 of the structural layer 556; and 4) one fourth rail 580is disposed between each pair of adjacent rails 568, 572, and 576, andextends from or at least generally proximate to the perimeter 560 (e.g.,within 50 μm of this perimeter 560, more preferably within 25 μm of thisperimeter 560) of the structural layer 556 toward, but not to, thecenter 564 of the structural layer 556. The second rails 572 extendfurther toward the center 564 than the third rails 576, and the thirdrails 576 extend further toward the center 564 than the fourth rails580.

[0116] Various layouts of etch release rails have been described above.However, it should be appreciated that these layouts are merelyrepresentative of the various ways in which etch release rails may bepatterned to define a plurality of etch release conduits. Any layout ofetch release rails may be utilized that will allow for the removal ofone or more sacrificial layers in a desired manner by providing orallowing for the formation of a plurality of at least generallylaterally extending etch release conduits or channels within one or moresacrificial layers through which an appropriate etchant may flow duringthe release of the corresponding microstructure from its substrate. Whatetch release rail layouts are appropriate for this purpose is based upona number of factors. Generally, the etchant will proceed at leastgenerally perpendicularly away from its corresponding etch releaseconduit. At least one and more typically a pair of etch release conduitswill extend at least generally along the lateral extent of each etchrelease rail. A targeted total etch release time will be established orspecified. The maximum total etch release time for the types ofmicrostructures described herein is preferably that which does notsignificantly damage any of the structural layers of the correspondingmicrostructure by exposure of the same to the etchant. The etch ratewill also be known and for design purposes may be assumed to beconstant. Therefore, a determination may then be made as to how far froma given etch release conduit the etchant will proceed in the specifiedtotal etch release time to create what may be characterized as aprojected etch release void. So long as the projected etch release voidsbetween adjacent etch release rails abut or more preferably overlap to adegree, or stated another way such that the entirety of the spacebetween adjacent etch release rails is defined by at least one and moretypically a plurality of projected etch release voids, the proposedlayout of the etch release rails will be appropriate for affecting therelease.

[0117] Another way to characterize an appropriate layout of etch releaserails is in relation to a maximum desired spacing between adjacentmostetch release rails. Each etch release rail should be positioned suchthat the maximum space between a given etch release rail and anadjacentmost etch release rail is no more than about twice the lineardistance that an etchant will proceed through a sacrificial layer in aspecified total etch release time. In one embodiment, this maximumspacing is less than about 100 microns, and in another embodiment iswithin a range of about 50-75 microns.

[0118] Another important factor in relation to the various mirrormicrostructures discussed above, as well as in relation to the methodsand mirror microstructures to be discussed below, is the surfacetopography of the uppermost structural layer of these mirrormicrostructures. This is particularly an issue when reinforcingstructures extend or depend from the lower surface of this uppermoststructural layer. These types of structures are generally formed byfirst forming a plurality of apertures within a layer of sacrificialmaterial, and then depositing a structural material over this layer ofsacrificial material (discussed in more detail below). That portion ofthe structural material that is deposited within the apertures formed inthe layer of sacrificial material defines the reinforcing structures.The surface topography that is desired for the upper surface of theuppermost structural layer of any of the mirror microstructuresdescribed herein, as deposited, or stated another way before beingplanarized, is one where the maximum distance between any peak andvalley on the upper surface of this uppermost structural layer is lessthan the maximum thickness of this uppermost structural layer. This typeof surface topography allows the upper surface of the uppermoststructural layer to thereafter be planarized a reasonable amount toyield the desired degree of optical flatness.

[0119] There are a number of ways in which the desired surfacetopography can be realized for the case where reinforcing structuresextend from the lower surface of the uppermost structural layer of themirror microstructure. One is to form this uppermost structural layerfor the mirror microstructure to a sufficient thickness such thatappropriate planarization techniques (e.g., chemical mechanicalpolishing) may be utilized to reduce the surface roughness of thissurface to a desired level without an undesirable amount of thinning ofthis uppermost structural layer at any location. A sufficient thicknessfor the uppermost structural layer in this scenario is where thethickness of the uppermost structural layer is thicker than theunderlying layer of sacrificial material by an amount such that afterbeing planarized (e.g., by chemical mechanical polishing) to realize thedesired optical surface, the uppermost structural lay will still havesufficient mechanical integrity. Another option for the case when thethickness of the uppermost structural layer of the mirror microstructureis comparable to the thickness of the underlying layer of sacrificialmaterial is to control the width of the apertures in this layer ofsacrificial material that again are used to define the reinforcingstructures that extend or depend from the lower surface of the uppermoststructural layer of the mirror microstructure.

[0120] The mirror microstructures described herein that structurallyreinforce the uppermost structural layer, that have one or morestructures extending or depending from the lower surface of theuppermost structural layer for purposes of providing etch release rails,or both, have a desired surface topography on the uppermost structurallayer. This may be provided or realized by the sizing of the structuresthat extend or depend from the lower surface of the uppermost structurallayer. Generally, the maximum width of any individual structure thatextends or depends from the lower surface of the uppermost structurallayer (e.g., the width of a rail, the diameter of a post or column)should be less than twice the thickness of the uppermost structurallayer to provide the desired surface topography based solely on theselection of reinforcement structure width. This “thickness of theuppermost structural layer” is that thickness that is disposed above thedepending reinforcing structure, or stated another way the thickness ata location that is between any adjacent depending reinforcingstructures. This provides a desirable surface topography for theuppermost structural layer, namely one that may be planarized (e.g., bychemical mechanical polishing) a reasonable amount to yield a desireddegree of optical flatness while allowing the uppermost structural layerto retain sufficient mechanical integrity. These same principles may beapplied to any underlying structural layer of the mirror microstructureas well to improve the surface topography. It should be noted that themaximum width of the reinforcing structures that extend or depend fromthe lower surface of the uppermost structural layer becomes lessimportant as the ratio of the thickness of the uppermost structurallayer to the thickness of the underlying sacrificial layer increases.Therefore, some combination of structural layer thickness andreinforcement structure width may provide the noted desired surfacetopography as well.

[0121] The various reinforcing structures discussed above may be used atany level within a mirror microstructure. That is, even though aparticular reinforcing structure may have only been described herein inrelation to a two-layered structure does not mean that the same couldnot be used to structurally reinforce a single structural layer of amirror microstructure (i.e., so as to cantilever from the same) or tostructurally interconnect adjacent but spaced structural layers in amirror microstructure having three or more spaced structural layers.Moreover, any combination of the above-noted reinforcing structures maybe used in any combination in a microstructure having three or morespaced structural layers (e.g., to interconnect any two adjacent butspaced structural layers), or may cantilever from a lower surface of astructural layer to structurally reinforce the same in the generalmanner, for instance, of the microstructure 302 to be discussed below inrelation to the methodology of FIGS. 15A-G.

[0122] The above-noted reinforcing structures may also utilize anyappropriate vertical and/or horizontal cross-sectionalprofiles/configurations, and further may extend in the lateral dimensionin any appropriate manner (e.g., axially, sinusoidally, meandering,“zig-zagging”).

[0123] Although the above-noted reinforcing structures have beenillustrated as being at least generally perpendicular to aninterconnected structural layer(s), such need not be the case. Moreover,all reinforcing structures need not necessarily be disposed in the samevertical orientation (i.e., the same may be disposed at one or moredifferent angles relative to vertical).

[0124] It should be appreciated that the mirror microstructures 30, 58,106, 130, 166, 384, and 384′ discussed above may be incorporated intoany surface micromachined system and at any elevation within such asystem, and that these microstructures 30, 58, 106, 130, 166, 384, and384′ may be appropriate for applications other than as a mirror.Characterizing the various structural layers in these microstructures30, 58, 106, 130, 166, 384, and 384′ as “first,” “second” and the likealso does not necessarily mean that these are the first, second, or thelike structural layers that are deposited over the associated substrate,although such may be the case. It should also be appreciated that thecharacterization of the various structural layers of thesemicrostructures 30, 58, 106, 130, 166, 384, and 384′ as “first,”“second,” and the like also does not mean that the same must be“adjacent” structural layers in any surface micromachined system thatincludes these microstructures 30, 58, 106, 130, 166, 384, and 384′.There may be one or more intermediate structural layers that aredeposited over the associated substrate at an elevation that is betweenwhat has been characterized as “first” and “second” structural layers orthe like, although any such structural layers will have been removedfrom the area occupied by the microstructures 30, 58, 106, 130, 166,384, and 384′ (e.g., there may be one or more of structural layers thatare “off to the side” or laterally disposed relative to a givenmicrostructure for various purposes). It should also be appreciated thatthe various structural layers of the noted microstructures 30, 58, 106,130, 166, 384, and 384′ may also be defined by one or more structurallayers, such as involving multiple and spaced in time depositions.

[0125] One key advantage of the microstructures 30, 58, 106, 130, 166,384, and 384′ discussed above is their structurally reinforced nature.Some of these reinforcement alternatives may require etch release holesthrough one or more of the various structural layers depending upon theparticular manufacturing technique that is employed, which may degradethe performance of the microstructures 30, 58, 106, 130, 166, 384, and384′ in a given application (e.g., when functioning as a mirror in anoptical system, and where etch release holes are required for theuppermost structural layer because of the reinforcement structure thatwas utilized). A certain amount of degradation may be acceptable basedupon the enhanced structural rigidity realized by these microstructures,and in certain applications the existence of the noted etch releaseholes may be irrelevant or at least of reduced significance. However,certain of the reinforcement structures utilized by the above-notedmicrostructures may actually enhance the release of the microstructurefrom the associated substrate and altogether alleviate the need forvertically disposed etch release holes in one or more structural layers.These techniques will be discussed in more detail below in relation toFIGS. 12-15, 17, and 20.

[0126] The above-described structurally reinforced mirrormicrostructures will typically have a minimum surface area of about2,000 μm² with a minimum lateral dimension of about 50 μm for theoptically functional surface of the mirror microstructure (e.g., in thecase of a circular mirror microstructure, this minimum lateral dimensionwould be its diameter; in the case of a square mirror microstructure,this minimum lateral dimension would be the length of any of its foursides; in the case of a rectangular mirror microstructure, this minimumlateral dimension would be the length of the shortest of its foursides). Moreover, the above-described structurally reinforced mirrormicrostructures will utilize a structural layer with the opticallyfunctional surface that has a maximum film thickness of about 10 μm inone embodiment, and more typically about 6 μm in another embodiment.This “maximum film thickness” does not include the thickness of anyreinforcement structure that extends or depends from a lower surface ofthe relevant structural layer.

[0127] The actual amount by which the above-noted microstructures arestructurally reinforced is affected by one or more characteristics ofthe reinforcing structures that are used. There may be two extremes inrelation to the number or density of reinforcing structures that areused. The first is having a high density for the individual reinforcingstructures, which is limited only by the design rules and minimumdimensions of the process technology, as well as the ability to insurethat the etchant for the release can adequately access the sacrificialfilms for their removal. The second extreme is to go to a very sparse orlow density for the reinforcing structures, which gets to the point ofdoing limited reinforcing or stiffening of the associated structurallayer(s). The benefit of the former is to provide a maximum effect ofreinforcement or stiffening of the associated structural layer(s) ormicrostructure, but at the expense of density and therefore total massof the microstructure (i.e., in the case where the microstructure is amirror, the microstructure may be very stiff, but too massive to allowfor the use or realization of rapid switching speeds). Therefore, theoptimum spacing and size of the reinforcing structures will oftentimesbe an engineering compromise between stiffness and mass. If total massdoes not matter, but stiffness is at a premium, then using a highdensity for the reinforcing structures, as allowed by the design andprocessed rules, would be optimum for the particular application.However, if the microstructure is a mirror or some other structure whichmust switch or otherwise move at a relatively fast rate (e.g., insub-millisecond times), then a calculation of total mass versusavailable actuation forces will likely determine the appropriate densityfor the reinforcing structures. Mass may also be an issue for thosemicrostructures that are moved in relation to the physical size of anyassociated actuator, the amount of voltage required to accomplish thedesired movement, or both.

[0128] There are a number of ways in which the microstructures 30, 58,106, 130, 166, 384, and 384′ may be at least generally characterized.One or more of the microstructures 30, 58, 106, 130, 166, 384, and 384′may be characterized as including: 1) at least two separate and distinct(i.e., not interconnected and disposed in spaced relation) reinforcingstructures (e.g., at least two separate and discrete columns or posts;at least two separate and discrete rails); 2) at least two separate anddistinct reinforcing structures that are disposed at different andradially spaced locations or positions in the lateral dimension, or atleast two different portions of what may be characterized as a singlereinforcing structure (e.g., the “grid” defined by the rails 174 andrails 178 in the microstructure 166 of FIGS. 9A-B) being disposed atdifferent and radially spaced locations or positions in this lateraldimension; 3) having a ratio of d_(RS)/d_(SL) that is no more than about0.5, and thereby including a ratio of “0”, for instance where d_(RS) is“0” (i.e., where there is a reinforcing structure at the center of thestructural layer being structurally reinforced); or 4) or anycombination thereof. Visualization of the second noted characterizationmay be enhanced by a reference to the FIGS. 2-3 embodiment where atleast some of the plurality of columns 50 of the microstructure 30 areclearly disposed at a different distance from a center 42 of themicrostructure 30, as well as the FIGS. 9A-B embodiment where at leastsome of the rails 174 and at least some of the rails 178 are disposed atdifferent radial positions and are in spaced relation.

[0129] Another way of characterizing the microstructures 30, 58, 106,130, 166, 384, and 384′ is in relation to a radius of curvature RC ofthe uppermost structural layer (e.g., the amount by which the uppermoststructural layer is “bowed” or “dished”). The radius of curvature RC mayhave its center on either side of the uppermost structural layer in themicrostructures 30, 58, 106, 130, 166, 384, and 384′. That is, the uppersurface of the uppermost structural layer in the microstructures 30, 58,106, 130, 166, 384, and 384′ may be generally concave or generallyconvex. In one embodiment, the uppermost structural layer of themicrostructures 30, 58, 106, 130, 166, 384, and 384′ has a radius ofcurvature RC that is at least about 1 meter, and in another embodimentthat is at least about 2 meters. The reinforcement configuration used bythe microstructure 166 in a three-layered mirror microstructure has beenfabricated with a radius of curvature RC that is about 14 meters. Itshould be noted that increasing the stiffness of a microstructure doesnot in and of itself mean that the radius of curvature of an uppermoststructural layer of this microstructure will in turn be increased. Thatis, the case of a constant stress gradient through a plate or a beamleads to the same radius of curvature independent of thickness to firstorder. This then indicates that simple stiffening by adding thickness toa plate or a beam does not, in and of itself, necessarily lead to aflatter structure with a greater radius of curvature. However, thecomplex method of reinforcing microstructures in the manner disclosedherein can lead to significant internal stress compensation between andwithin the individual structural layers of these reinforcedmicrostructures, such that greater flatness (i.e., a larger radius ofcurvature for the uppermost structural layer) can be realized inaddition to achieving greater stifffiess.

[0130] Another characterization that can be made in relation to themicrostructures 30, 58, 106, 130, 166, 384, and 384′ is the effect ofthe various reinforcing structures/layouts on overall structuralstiffness of the microstructures 30, 58, 106, 130, 166 384, and 384′,which can be characterized by moment of inertia. In very general terms,the moment of inertia for a simple rectangular cross-section isI=bh³/12, where h is the plate thickness and b the width. Thisillustrates the general idea or concept that structural stiffness is acubic function of the corresponding thickness. Thus, going from a 2.25μm thick single structural layer to an approximately 11.0 μmmulti-layered, structurally reinforced microstructure of the typecontemplated by the microstruetures 30, 58, 106, 130, 166, 384, and 384′implies an approximate increase of stiffness by a factor of11³/2.25³=117, or roughly two orders of magnitude (with the orders by10-based). This is important when there is a need for a structure to notdeform out of plane, or in the case of a mirror microstructure that iscoated with a reflective gold layer to not be deformed by the stress inthe gold layer. In other words, because of thermal mismatch for example,the gold can be in relative tension to the underlying structural layer(e.g., polysilicon), and thus would have the tendency to cause theunderlying structural layer to curl into a cup shape. The dramaticincrease in stiffness by reinforcement will keep the mirrormicrostructure much flatter. Also, during temperature cycles, thegold-coated plate will not change its RC as much (i.e., it will be muchmore mechanically stable). The overall complexity of the geometry andthe deposition and anneal precludes a simple ‘estimate’ of the resultingRC especially at the current levels being obtained. Empiricaldetermination is less time consuming and more accurate.

[0131] Investigations are still being undertaken in relation toevaluating the structural reinforcement of the microstructures 30, 58,106, 130, 166, 384, and 384′. Generally, it is believed that astructurally reinforced three-layered microstructure will be more rigidthan a structurally reinforced two-layered microstructure. In this case,any combination of the above-noted reinforcing structures thatstructurally interconnect adjacent structural layers in themicrostructures 30, 58, 106, 130, 166, 384, and 384′ may be utilized ina three-layered microstructure in accordance with one or more principlesof the present invention. However, evaluations are still ongoing inrelation to “optimizing” the structural reinforcement of themicrostructures 30, 58, 106, 130, 166, 384, and 384′ in the generalmanner described herein. There may be instances where differentcombinations of the above-noted reinforcing structures may be moreappropriate for when the associated microstructure is used in a givenapplication or in certain conditions.

[0132] Various microstructure fabrication methods will now be described.Each of the various fabrication methods to be discussed that utilizereinforcement/etch release rails may also use the above-noted guidelinesfor maximum reinforcement structure widths to realize the desiredsurface topography for the uppermost structural layer prior toplanarizing the same. Each of the various fabrication methods to bediscussed which define etch release conduits should be implemented suchthat at least one end of at least one etch release conduit is disposedat or at least generally proximate to a perimeter of the microstructurebeing fabricated (e.g., within 50 microns of this perimeter in oneembodiment, and more preferably within 25 microns of this perimeter inanother embodiment). This again reduces the amount of time that therelease etchant must “etch in” from this perimeter before reaching theetch release conduit(s), and thereby allows the release to be finishedwithin a desired amount of time. Multiple ends of etch release conduitsor etch release conduit accesses are preferably disposed at this radialposition. It should be noted that sacrificial material is disposed aboutthe perimeter of the microstructures that are fabricated in accordancewith the following. Therefore, absent a preformed via or the like, therelease etchant must first etch down to the level(s) at which the etchrelease conduits are disposed. However, the time required for therelease etchant to go down to the level(s) of the etch release conduitsis not that significant due to the rather minimal vertical distancewhich these microstructures extend above their corresponding substrate.

[0133] One method for making a microstructure is illustrated in FIGS.12A-M. This methodology may be utilized to make the mirrormicrostructure 106 of FIGS. 5-6, and the principles of this methodologymay be utilized in/adapted for the manufacture of the mirrormicrostructure 130 of FIG. 7, the mirror microstructure 384 of FIGS.10A-C, and the mirror microstructure 384′ of FIG. 10D, as well as thevariations therefore that are presented in FIGS. 11A-F. In addition tobeing able to form a desired reinforcing structure, the methodology ofFIGS. 12A-M further provides a desired manner for releasing themicrostructure at the end of processing by forming a plurality of atleast generally laterally extending etch release conduits in one or moreof its sacrificial layers to facilitate the removal thereof to providethe releasing function.

[0134]FIG. 12A illustrates a substrate 182 on which a microstructure 180(FIG. 12M) will be fabricated by surface micromachining techniques.Multiple layers are first sequentially deposited/formed over thesubstrate 182. A first sacrificial layer 186 is deposited over thesubstrate 182 as illustrated in FIG. 12B, a first structural layer 190is deposited on the first sacrificial 186 as illustrated in FIG. 12C,and a second sacrificial layer 194 is deposited on the first structurallayer 190 as illustrated in FIG. 12D. The second sacrificial layer 194is then patterned to define a plurality of interconnect apertures 198 asillustrated in FIG. 12E. These interconnect apertures 198 at a minimumallow for establishing a structural connection with the first structurallayer 190, and may be in the form of at least generally laterallyextending grooves or trenches (e.g., to define a plurality of rails orat least the lower portion thereof, such as the type utilized by themirror microstructure 106 of FIG. 5, the mirror microstructure 130 ofFIG. 7, and the mirror microstructure 384 of FIG. 10A, as well as thevariations therefore illustrated in FIGS. 11A-F). These interconnectapertures 198 could also be in the form of a plurality of separate anddiscrete holes that are disposed in spaced relation to define aplurality of posts or columns that would structurally interconnect withthe underlying first structural layer 190 (e.g., similar to the mannerin which the columns 50 interconnect with the underlying firststructural layer 34 in the case of the mirror microstructure 30 of FIG.2A). Using the methodology of FIGS. 12A-M to make the mirrormicrostructure 384 of FIGS. 10A-C or the mirror microstructure 384′ ofFIG. 10D would not require this type of a patterning of the secondsacrificial layer 194 to define the plurality of interconnect apertures198, since the rails 396 of the microstructure 384/384′ do notinterconnect with any underlying structural layer.

[0135] A second structural layer 202 is deposited on the secondsacrificial layer 194 as illustrated in FIG. 12F. The material thatdefines the second structural layer 202 is also deposited within and atleast substantially fills the interconnect apertures 198 that werepreviously formed in the second sacrificial layer 194, and such may becharacterized as being part of the second structural layer 202. Thisportion of the second structural layer 202 may be characterized as aplurality of first reinforcement sections 214 that will be the lowerextreme of a reinforcing assembly 208 for the microstructure 180 that isbeing fabricated. Although FIG. 12F shows an intersection between thelower extreme of each of the first reinforcement sections 214 and theupper extreme of the first structural layer 190, typically such anintersection will not exist and instead will at least appear to becontinuous.

[0136] The second structural layer 202 is then patterned to define aplurality of at least generally laterally extending second reinforcementsections 210 for the reinforcing assembly 208, as illustrated in FIG.12G (e.g., to define a plurality of rails or at least the middle portionthereof of the type utilized by the microstructure 106 of FIG. 5, themicrostructure 130 of FIG. 7, the microstructure 384 of FIGS. 10A-C, andthe microstructure 384′ of FIG. 10D, as well as the variations thereforepresented in FIGS. 11A-F). Each second reinforcement section 210 isdisposed directly above (e.g., vertically aligned) with at least onefirst reinforcement section 214 (if used), although the secondreinforcement sections 210 will typically have a slightly larger widththan any corresponding first reinforcement section(s) 214.

[0137] A third sacrificial layer 218 is then deposited on the secondreinforcement sections 210 that were formed from the second structurallayer 202 as illustrated in FIG. 12H. The upper surface of this thirdsacrificial layer 218 will typically have a wavy or uneven contour.Generally, those portions of the third sacrificial layer 218 that aredisposed over the second reinforcement sections 210 will be disposed ata higher elevation than those portions of the third sacrificial layer218 that are disposed between adjacent second reinforcement sections210. Therefore, the upper surface of the third sacrificial layer 218will typically be planarized in an appropriate manner, such as bychemical mechanical polishing to yield a sufficiently flat upper surfacefor the third sacrificial layer 218, as illustrated in FIG. 12I.

[0138] The third sacrificial layer 218 is then patterned to define aplurality of interconnect apertures 222 as illustrated in FIG. 12J.These interconnect apertures 222 at a minimum allow for establishing astructural interconnection with the second reinforcement sections 210,and may be in the form of at least generally laterally extending groovesor trenches (e.g., to define a plurality of rails or at least the upperportion thereof of the type utilized by the microstructure 106 of FIG.5, the microstructure 130 of FIG. 7, and the microstructure 384 of FIG.10A, as well as the variations therefore illustrated in FIGS. 11A-F), ormay be in the form of a plurality of separate and discrete holes thatare disposed in spaced relation (e.g., to define a plurality of posts orcolumns of the type utilized by the mirror microstructure 384′ of FIG.10D). Each interconnect aperture 222 is disposed directly above (e.g.,vertically aligned) a corresponding second reinforcement section 210,although the second reinforcement sections 210 will typically have aslightly larger width than their corresponding interconnect aperture(s)222.

[0139] A third structural layer 226 is deposited on the thirdsacrificial layer 218 as illustrated in FIG. 12K. The material thatdefines the third structural layer 226 is also deposited within and atleast substantially fills the interconnect apertures 222 that werepreviously formed in the third sacrificial layer 218, and such may becharacterized as being part of the third structural layer 226. Thisportion of the third support layer 226 may be characterized as aplurality of third reinforcement sections 230 that are the upper extremeof the reinforcing assembly 208 for the microstructure 180 that is beingfabricated. Although FIG. 12K shows an intersection between the lowerextreme of each of the third reinforcement section 230 and the upperextreme of their corresponding second reinforcement 210, typically suchan intersection will not exist and instead will at least appear to becontinuous.

[0140] The upper surface of the third structural layer 226 willtypically have a wavy or uneven contour as illustrated in FIG. 12K.Generally, those portions of the third structural layer 226 that aredisposed between adjacent third reinforcement sections 230 will berecessed to a degree. Therefore, the upper surface of the thirdstructural layer 226 will typically be planarized in an appropriatemanner, such as by chemical mechanical polishing, to yield asufficiently flat upper surface for the third structural layer 226 asillustrated in FIG. 12L. This completes the definition of themicrostructure 180. It should be appreciated that the system thatincludes the microstructure 180 will likely include other componentsthan those illustrated in FIGS. 12A-M and that may interface with themicrostructure 180 in some manner (e.g., one or more actuators).

[0141] The microstructure 180 is now ready to be released. “Released”means to remove each of the sacrificial layers of the surfacemicromachined system and thereby including the first sacrificial layer186, the second sacrificial layer 194, and the third sacrificial layer218. An etchant is used to provide the releasing function. The manner inwhich the microstructure 180 was formed in accordance with themethodology of FIGS. 12A-M reduces the time required for the sacrificiallayers 194 and 218 to be totally removed. Ultimately, a plurality of atleast generally laterally extending etchant flow pipes, channels, orconduits are formed in the third sacrificial layer 218. Those portionsof the third sacrificial layer 218 that are positioned against/near thesecond reinforcement sections 210 that were formed from the secondstructural layer 202 are believed to be less dense than the remainder ofthe third sacrificial layer 218 since the etch rate is greater inproximity to the second reinforcement sections 210 and including alongthe length thereof. Recall that the third sacrificial layer 218 wasdeposited after the second reinforcement sections 210 were formed, whichcreates these low density regions. Low density regions in the thirdsacrificial layer 218 thereby exist along the entire length of bothsides of each second reinforcement 210. Principally these low densityregions will exist along a sidewall 212 of each of the secondreinforcement section 210 (e.g., the vertically disposed/extendingportion of the second reinforcement section 210). The etch rate will begreater in the low density regions of the third sacrificial layer 218than throughout the remainder of the third sacrificial layer 218. Thiswill effectively form at least two etch release pipes, channels orconduits in the third sacrificial layer 218 along the side of eachsecond reinforcement section 210. The development of the etch releasechannels during the initial portion of the release etch provides accessto interiorly disposed locations within the sacrificial layers for theetchant to complete the release before the etchant has any significantadverse effect on the microstructure 180. Notwithstanding thecharacterization of the structures 214, 210, and 230 as “reinforcementsections,” it should be appreciated that the entire focus of themethodology of FIGS. 12A-M could in fact be to simply provide aplurality of at least generally laterally extending etch releaseconduits, to in turn provide a “rapid etch release function” for themicrostructure 180. That is, it is not required that the structures 214,210, and 230 actually structurally reinforce the microstructure 180,although such is preferably the case. Therefore, the structures 210 thatprovide for the definition of the low density regions in the thirdsacrificial layer 218, and thereby the etch release conduits, could alsobe properly characterized as etch release rails or the like.

[0142] The microstructure 180 of FIG. 12M has a desired surfacetopography on its third structural layer 226 using the above-notedprinciples. For the case where the thickness of third structural layer226 is comparable or less than the thickness of the underlying thirdsacrificial layer 218, the maximum lateral dimension of any rail uppersection 230 (designated as “w” in FIG. 12M) again should be less thantwice the thickness of the uppermost structural layer (designated as “t”in FIG. 12M, and which does not include the depending structure). Thisagain provides a desirably smooth surface topography for the thirdstructural layer 226, which is desired for optical applications. Havingthe third structural layer 218 be of a thickness which is greater thanthe thickness of the third sacrificial layer 218 reduces the effects ofthe width of the interconnect apertures 222 on the surface topography ofthe third structural layer 218.

[0143] The basic principle for forming etch release channels or conduitsencompassed by the methodology represented in FIGS. 12A-M is that lowdensity regions of sacrificial material are formed when the sacrificialmaterial is deposited along at least generally vertically disposedsurfaces of an etch release rail, and that the same each effectivelydefines a etch release channel or conduit. These etch release rails mayexist at any desired level within the microstructure being fabricatedand yet still provide this low density region formation function.Moreover, these etch release rails do not need to be structurallyinterconnected with the uppermost structural layer of the microstructurebeing fabricated to provide this low density region formation function.For instance, these etch release rails instead could be anchored to theunderlying substrate or another underlying structural layer. In fact,these etch release rails need not remain in the final structure of themicrostructure being fabricated at all, but instead may be removedduring the release of the microstructure from the substrate.

[0144] Another method for making a microstructure is illustrated inFIGS. 13A-M. This methodology may be utilized to make the mirrormicrostructure 106 of FIGS. 5-6, and the principles of this methodologymay be utilized in/adapted for the manufacture of the mirrormicrostructure 130 of FIG. 7, the mirror microstructure 384 FIGS. 10A-C,and the mirror microstructure 384′ of FIG. 10D, as well as thevariations therefore presented in FIGS. 11A-F. In addition to being ableto form a desired reinforcing structure, the methodology of FIGS. 13A-Mfurther provides a desired manner for releasing the microstructure atthe end of processing by forming a plurality of at least generallylaterally extending etch release conduits in one or more of itssacrificial layers to facilitate the removal thereof to provide thereleasing function. In contrast to the methodology of FIGS. 12A-M, themethodology of FIGS. 13A-M forms these etch release conduits during thefabrication of the microstructure (i.e., there is at least one moredeposition after these etch release conduits are formed). Stated anotherway, the plurality of etch release in the case of the methodology ofFIGS. 13A-M exist before the microstructure and sacrificial layers areexposed to any etchant for providing the release function.

[0145]FIG. 13A illustrates a substrate 234 on which a microstructure 232will be fabricated. Multiple layers are first sequentiallydeposited/formed over the substrate 234. A first sacrificial layer 238is deposited over the substrate 234 as illustrated in FIG. 13B, a firststructural layer 242 is deposited on the first sacrificial layer 238 asillustrated in FIG. 13C, and a second sacrificial layer 246 is depositedon the first structural layer 242 as illustrated in FIG. 13D. The secondsacrificial layer 246 is then patterned to define a plurality ofinterconnect apertures 250 as illustrated in FIG. 13E. Theseinterconnect apertures 250 at a minimum allow for establishing astructural connection with the first structural layer 242, and may be inthe form of at least generally laterally extending grooves or trenches(e.g., to define a plurality of rails or at least the lower portionthereof of the type utilized by the microstructure 106 of FIG. 5 and themicrostructure 130 of FIG. 7, as well as the variations thereforeillustrated in FIGS. 11A-F). The interconnect apertures 250 could alsobe in the form of a plurality of separate and discrete holes that aredisposed in spaced relation to define a plurality of posts or columnsthat would structurally interconnect with the underlying firststructural layer 242 (e.g., similar to the manner in which the columns50 interconnect with the underlying first structural layer 34 in thecase of the mirror microstructure 30 of FIG. 2A). Using the methodologyof FIGS. 13A-M to make the microstructure 384 of FIGS. 10A-C andmicrostructure 384′ of FIG. 10D would not require this patterning of thesecond sacrificial layer 246 to define the plurality of interconnectapertures 250, since the rails 396 of the microstructure 384/384′ do notinterconnect with an underlying structural layer.

[0146] A second structural layer 254 is deposited on the secondsacrificial layer 246 as illustrated in FIG. 13F. The material thatdefines the second structural layer 254 is also deposited within and atleast substantially fills the interconnect apertures 250 that werepreviously formed in the second sacrificial layer 246, and such may becharacterized as being part of the second structural layer 254. Thisportion of the second support layer 254 may be characterized as aplurality of first reinforcement sections 258 that are the lower extremeof a reinforcing assembly 256 for the microstructure 232 that is beingfabricated (FIG. 13M). Although FIG. 13F shows an intersection betweenthe lower extreme of each of the first reinforcement sections 258 andthe upper extreme of the first structural layer 242, typically such anintersection will not exist and instead will at least appear to becontinuous.

[0147] The second structural layer 254 from FIG. 13F is then patternedto define a plurality of at least generally laterally extending secondreinforcement sections 262 for the reinforcing assembly 256 (FIG. 13M),as illustrated in FIG. 13G (e.g., to define a plurality of rails or atleast the middle portion thereof of the type utilized by themicrostructure 106 of FIG. 5, the microstructure 130 of FIG. 7, themicrostructure 384 of FIGS. 10A-C, and the mirror microstructure 384′ ofFIG. 10D, as well as the variations therefore presented in FIGS. 11A-F).Each second reinforcement section 262 is disposed directly above (e.g.,vertically aligned) with at least one first reinforcement section 258(if any), although the second reinforcement sections 262 will typicallyhave a slightly larger width than their corresponding firstreinforcement section(s) 258 (if any). At this time an upper portion ofthe second sacrificial layer 246 is removed as illustrated in FIG. 13H.That is, a portion of the second sacrificial layer 246 remains afterthis removal operation. The second sacrificial layer 246 extends abovethe first structural layer 242 a distance which is less than thedistance which the lower extreme of the second reinforcement sections262 are disposed above the first structural layer 242. As, there is nowa gap or an undercut 266 beneath the lower extreme of the secondreinforcement sections 262 and the upper surface of the secondsacrificial layer 246. One way in which only an upper portion of thesecond sacrificial layer 246 may be removed is by a timed or controlledetch. It is also basically a requirement that this etch be of anisotropic type in order to form the undercuts 266. This is most easilyaccomplished using a liquid HF-based etchant. An anisotropic dry plasmaetch, for example, would only etch straight down and the undercuts 266(and thereby the etch release channels 270 noted below) would notsubsequently be formed.

[0148] A third sacrificial layer 274 is then deposited on the secondreinforcement sections 262 that were formed from the second structurallayer 254 and on the second sacrificial layer 246 as illustrated in FIG.13I. Although FIG. 131 shows an intersection between the thirdsacrificial layer 274 and the second sacrificial layer 246, typicallythis will not be the case such that the third sacrificial layer 274 andthe second sacrificial layer 246 will appear to be continuous. Not allportions of the undercuts 266 will “fill” with the material that definesthe third sacrificial layer 274, for example if the formation of thethird sacrificial layer 274 is done with a PECVD oxide. These resultingvoids define a plurality of at least generally laterally extending etchrelease channels 270. One of these etch release channels 270 is disposedon and extends along the entire length of each side of an upper extremeof the first reinforcement sections 258 of the reinforcing assembly 256(and/or beneath the second reinforcement sections 262 along both sidesthereof).

[0149] The upper surface of the third sacrificial layer 274 may retain awavy or uneven contour after being deposited. The upper surface of thethird sacrificial layer 274 may then be planarized in an appropriatemanner, such as by chemical mechanical polishing, to yield asufficiently flat upper surface for the third sacrificial layer 274 andas illustrated in FIG. 13I. In any case, the third sacrificial layer 274is then patterned to define a plurality of interconnect apertures 278 asillustrated in FIG. 13J. These interconnect apertures 278 at a minimumallow for establishing a structural interconnection with the secondreinforcement sections 262, and may be the form of at least generallylaterally extending grooves or trenches (e.g., to define a plurality ofrails or at least the upper portion thereof of the type utilized by themicrostructure 106 of FIG. 5, the microstructure 130 of FIG. 7, and themicrostructure 384 of FIGS. 10A-C, as well as the variations thereforeillustrated in FIGS. 11A-F), or may be in the form of a plurality ofseparate and discrete holes that are disposed in spaced relation (e.g.,to define a plurality of posts or columns of the type utilized by themicrostructure 384′ of FIG. 10D). In any case, each interconnectaperture 278 is disposed directly above (e.g., vertically aligned) witha corresponding second reinforcement section 262, although the secondreinforcement sections 262 will typically have a slightly larger widththan their corresponding interconnect aperture(s) 278.

[0150] A third structural layer 282 is then deposited on the thirdsacrificial layer 274 as illustrated in FIG. 13K. The material thatdefines the third structural layer 282 is also deposited within and atleast substantially fills the interconnect apertures 278 that werepreviously formed in the third sacrificial layer 274, and such may becharacterized as being part of the third structural layer 282. Thisportion of the third structural layer 282 may be characterized as aplurality of third reinforcement sections 286 that are the upper extremeof the reinforcing assembly 256 for the microstructure 232 that is beingfabricated. Although FIG. 13K shows an intersection between the lowerextreme of each of the third reinforcement sections 286 and the upperextreme of their corresponding second reinforcement section 262,typically such an intersection will not exist and instead will at leastappear to be a continuous structure.

[0151] The upper surface of the third structural layer 282 willtypically have a wavy or uneven contour, such as a plurality oflaterally disposed and axially extending depressions. Generally, thoseportions of the third structural layer 282 that are disposed betweenadjacent third reinforcement sections 286 will be recessed to a degree.Therefore, the upper surface of the third structural layer 282 willtypically be planarized in an appropriate manner, such as by chemicalmechanical polishing, to yield a sufficiently flat upper surface for thethird structural layer 282 and as illustrated in FIG. 13L. Thiscompletes the definition of the microstructure 232. It should beappreciated that the system that includes the microstructure 232 willlikely include other components than those illustrated in FIGS. 13A-Mand that may interface with the microstructure 232 in some manner (e.g.,one or more actuators).

[0152] The microstructure 232 is now ready to be released. “Released”means to remove each of the sacrificial layers in the system, andthereby including the first sacrificial layer 238, the secondsacrificial layer 246, and the third sacrificial layer 274. An etchantis used to provide the releasing function. Predefined flow paths forthis etchant are defined in and extend through portions of the secondsacrificial layer 246 and the third sacrificial layer 274 in the form ofthe above-noted etch release channels 270. The existence of the etchrelease channels 270 provides access to interiorly disposed locationswithin the sacrificial layers 246, 274 for the etchant to complete therelease before the etchant has any significant adverse effect on themicrostructure 232. Notwithstanding the characterization of thestructures 258, 262, and 286 as “reinforcement sections,” it should beappreciated that the entire focus of the methodology of FIGS. 13A-Mcould in fact be to simply provide a plurality of at least generallylaterally extending etch release conduits, to in turn provide a “rapidetch release function” for the microstructure 232. That is, it is notrequired that the structures 258, 262, and 286 actually structurallyreinforce the microstructure 232, although such is preferably the case.Therefore, the structures 258 and/or 262 that provide for the definitionof the etch release conduits 270 could also be properly characterized asetch release rails or the like.

[0153] The basic principle for forming etch release channels or conduitsencompassed by the methodology represented in FIGS. 13A-M is that one ormore undercuts may be formed under an etch release rail in such a mannerthat the subsequent deposition of a sacrificial material will notentirely fill these undercuts, thereby leaving a void that defines anetch release channel or conduit. These etch release rails may exist atvarious levels within the microstructure being fabricated and yet stillallow for the formation of etch release channels or conduits in thissame general manner. Moreover, these etch release rails do not need tobe structurally interconnected with the uppermost structural layer ofthe microstructure being fabricated to allow for the formation of etchrelease channels or conduits in this same general manner. For instance,these etch release rails instead could be anchored to the underlyingsubstrate or another underlying structural layer. In fact, these etchrelease rails need not remain in the final structure of themicrostructure being fabricated at all, but instead may be removedduring the release of the microstructure from the substrate as in thecase of the methodology of FIGS. 14A-F.

[0154] Another method for making another embodiment of a microstructure358 is illustrated in FIGS. 14A-F. FIG. 14A illustrates that a firstsacrificial layer 360 has been deposited over a substrate 356, and thatan intermediate layer 364 has been deposited directly on the firstsacrificial layer 360. The first sacrificial layer 360 is formed from adifferent material than the intermediate layer 364. In one embodiment,the first sacrificial layer 360 is formed from those types of materialsidentified above as being appropriate for the types of sacrificiallayers described herein, while the intermediate layer 364 may bematerials such as silicon nitride, polygermanium, or the like. Thematerial that is selected for the intermediate layer 364 should be atleast partially soluble in the etchant that is used to remove the firstsacrificial layer 360, or in a secondary etchant that does not affectthe various structural layers of the microstructure 358 and that can beapplied after the release etchant. For example, if polygermanium wereused for the intermediate layer 364, it will not dissolve in a releaseetch that uses HF, but could be dissolved subsequently in a shorthydrogen peroxide bath that would not adversely affect the polysiliconthat may be used for the various structural layers of the microstructure358. In any case, of the intermediate layer 364 is then patterned todefine a plurality of at least generally laterally extending strips 368as illustrated in FIG. 14B, and which function as etch release rails. Assuch, any of the layouts noted above for etch release rails may beutilized. However, unlike other etch release rails described herein thatalso provide a reinforcing function, the strips 368 will be removedduring the release of the microstructure 358 that is formed by themethodology of FIGS. 14A-F. In order to ensure the complete removal ofthe strips 368, they should be of a reduced thickness. In oneembodiment, the thickness or vertical extent of the silicon nitridestrips 368 is no more than about 1500 Å.

[0155] At this time, part of an upper portion of the first sacrificiallayer 360 is removed as illustrated in FIGS. 14C. Generally, a portionof the first sacrificial layer 360 is removed from under the pluralityof strips 368 along both of its edges to define a gap or an undercut 370along both edge portions of each strip 368. The entirety of the firstsacrificial layer 360 remains directly under a portion of the strips 368in the form of a pedestal or the like to support the same. One way inwhich only an upper portion of the first sacrificial layer 360 may beremoved is by a timed or controlled etch. It is also basically arequirement that this etch be of an isotropic type in order to form theundercuts 370. This is most easily accomplished using a liquid HF-basedetchant. An anisotropic dry plasma etch, for example, would only etchstraight down and the undercuts 370 (and thereby the etch releasechannels 380 noted below) would not subsequently be formed.

[0156] A second sacrificial layer 372 is then deposited on the strips368 and on the first sacrificial layer 360 as illustrated in FIG. 14D.Although FIG. 14D shows an intersection between the second sacrificiallayer 372 and the first sacrificial layer 360, typically this will notbe the case such that the second sacrificial layer 372 and the firstsacrificial layer 360 will appear to be continuous. Not all portions ofthe undercuts 370 will “fill” with the material that defines the secondsacrificial layer 372, for example if the formation of the secondsacrificial layer 372 is done with a PECVD oxide. These resulting voidsdefine a plurality of at least generally laterally extending etchrelease channels 380. One of these etch release channels 380 is disposedon and extends along the entire length of each bottom side portion ofeach of the strips 368.

[0157] The upper surface of the second sacrificial layer 372 may retaina wavy or uneven contour after being deposited (not shown). The uppersurface of the second sacrificial layer 372 may then be planarized in anappropriate manner, such as by chemical mechanical polishing, to yield asufficiently flat upper surface for the third sacrificial layer 372 andas illustrated in FIG. 14D. In any case, a first structural layer 376 isdeposited on the second sacrificial layer 372 as illustrated in FIG. 14Ewhich defines the entirety of a microstructure 358. It should beappreciated that the system that includes the microstructure 358 willlikely include other components than those illustrated in FIGS. 14A-Fand that may interface with the microstructure 358 in some manner (e.g.,one or more actuators).

[0158] The microstructure 358 is now ready to be released. “Released”means to remove each of the sacrificial layers in the system, andthereby including the first sacrificial layer 360 and the secondsacrificial layer 372. The plurality of strips 368 are also removed inthis release. Etchants are used to provide the releasing function.Predefined flow paths for this etchant are defined in and extend throughportions of the second sacrificial layer 372 and the first sacrificiallayer 360 in the form of the above-noted etch release channels 380. Theexistence of the etch release channels 380 provides access to interiorlydisposed locations within the sacrificial layers 360, 372 for theetchant to complete the release before the etchant has any significantadverse effect on the microstructure 358.

[0159] The manner in which the etch release channels 380 are formed issimilar to the methodology of FIGS. 13A-M. The primary difference isthat the methodology of FIGS. 14A-F does not define any reinforcingstructure for its microstructure 358, whereas the methodology of FIGS.13A-M does define a reinforcing assembly 256 for its microstructure 232.A related difference is that the strips 368 in the methodology of FIGS.14A-F are removed during the release etch or in a post-release etch,whereas the reinforcing assembly 256 in the methodology of FIGS. 13A-Mis not removed during the release.

[0160] Another method for making another embodiment of a reinforcedmicrostructure 302 is illustrated in FIGS. 15A-G. In addition to beingable to form a desired reinforcing structure, the methodology of FIGS.15A-G further provides a desired manner for releasing the microstructure302 at the end of processing by forming a plurality of at leastgenerally laterally extending etch release channels in one or more ofits sacrificial layers to facilitate the removal thereof when releasingthe microstructure 302. Any of the layouts noted above for etch releaserails may be used to form these etch release channels, but in the mannerset forth in relation to FIGS. 15A-G.

[0161]FIG. 15A illustrates a substrate 300 on which the microstructure302 will be fabricated. Multiple layers are first sequentiallydeposited/formed over the substrate 300. A first sacrificial layer 304is deposited over the substrate 300, and a first structural layer 308 isthen deposited on the first sacrificial layer 304. The first supportlayer 308 is then patterned to define a plurality of lower reinforcementsections 312 of a reinforcing assembly 310 for the microstructure 302 asillustrated in FIG. 15B. These lower reinforcement sections 312 are atleast generally laterally extending. Adjacent lower reinforcementsections 312 are separated by a spacing 314 that is also thereby atleast generally laterally extending as well. Generally, a relationshipbetween the distance between adjacent lower reinforcement sections 312and the height or vertical extent of the lower reinforcement sections312 is selected to allow a plurality of etch release channels to bedefined in the spacings 314. In one embodiment: 1) the width or lateralextent of each of the spacings 314, or stated another way the distancebetween adjacent lower reinforcement sections 312 measured parallel withan upper surface of the substrate 300, is no more than about 1.5 μm; and2) the height or vertical extend of each of the lower reinforcementsections 312 is at least about 1.5 μm. Stated another way, a ratio ofthe height of a given lower reinforcement section 312 to a width orlateral extent between this lower reinforcement section 312 and anadjacent lower reinforcement section 312 (i.e., one of the rail spacings314) is at least about 1:1.

[0162] A second sacrificial layer 316 is deposited on the firststructural layer 308 as illustrated in FIG. 15C. The second sacrificiallayer 316 extends within and occupies a portion of each of the spacings314 that were previously formed from the first structural layer 308.However, the material that defines the second sacrificial layer 316 doesnot fill or occupy the entirety of the spacings 314 due to the relativeclose spacing between adjacent lower reinforcement sections 312 inrelation to the height or vertical extent of the lower reinforcementsections 312. This may be characterized as “keyholing.” In any case, theremaining voids in the lower portion of each of the spacings 314 definea plurality of at least generally laterally extending etch releasechannels 320.

[0163] The upper surface of the second sacrificial layer 316 may retaina wavy or uneven contour. The upper surface of the second sacrificiallayer 316 may then be planarized in an appropriate manner, such as bychemical mechanical polishing, to yield a sufficiently flat uppersurface for the second sacrificial layer 316 and as illustrated in FIG.15C. In any case, the second sacrificial layer 316 is then patterned todefine a plurality of interconnect apertures 324 as illustrated in FIG.15D. These interconnect apertures 324 at a minimum allow forestablishing a structural connection with the lower reinforcementsections 312, and may be in the form of at least generally laterallyextending grooves or trenches (e.g. to define rails), or may be in theform of a plurality of separate and discrete holes that are disposed inspaced relation (e.g. to define a plurality of columns or posts). In anycase, each interconnect aperture 324 is disposed directly above (e.g.,vertically aligned) a corresponding lower reinforcement section(s) 312,although the lower reinforcement sections 312 will typically have aslightly larger width than their corresponding interconnect aperture(s)324.

[0164] A second structural layer 328 is deposited on the secondsacrificial layer 316 as illustrated in FIG. 15E. The material thatdefines the second structural layer 328 is also deposited within and atleast substantially fills the interconnect apertures 324 that werepreviously formed in the second sacrificial layer 316, and such may becharacterized as being part of the second structural layer 328. Thisportion of the second structural layer 328 may be characterized as aplurality of upper reinforcement sections 332 that are the upper extremeof the reinforcing assembly 310 (FIG. 15G) for the microstructure 302that is being fabricated. Although FIG. 15E shows an intersectionbetween the lower extreme of each of the upper reinforcement sections332 and the upper extreme of their corresponding lower reinforcementsection 312, typically such an intersection will not exist and insteadwill at least appear to be a continuous structure.

[0165] The upper surface of the second structural layer 328 willtypically have a wavy or uneven contour or at least a plurality oflaterally disposed and preferably axially extending depressions.Generally, those portions of the second structural layer 328 that aredisposed between adjacent upper reinforcement sections 332 will berecessed to a degree. Therefore, the upper surface of the secondstructural layer 328 will typically be planarized in an appropriatemanner, such as by chemical mechanical polishing, to yield asufficiently flat upper surface for the second structural layer 328 andas illustrated in FIG. 15F. This completes the definition of themicrostructure 302. It should be appreciated that the system thatincludes the microstructure 302 will likely include other componentsthan those illustrated in FIGS. 15A-G and that may interface with themicrostructure 302 in some manner (e.g., one or more actuators).

[0166] The microstructure 302 is now ready to be released. “Released”means to remove each sacrificial layer and thereby including the firstsacrificial layer 304 and the second sacrificial layer 316. An etchantis used to provide the releasing function. Predefined flow paths forthis etchant are defined in and extend through portions of the firstsacrificial layer 304 and the second sacrificial layer 316 in the formof the above-noted etch release channels 320. The existence of the etchrelease channels 320 provides access to interiorly disposed locationswithin the sacrificial layers for the etchant to complete the releasebefore the etchant has any significant adverse effect on themicrostructure 302.

[0167] As opposed to other of the reinforced microstructures disclosedherein, the microstructure 302 is only a single structural layer (secondstructural layer 328) that is structurally reinforced by a plurality of“cantilevered” structures extending downwardly therefrom, namely theplurality of at least generally laterally extending lower reinforcementsections 312. Notwithstanding the characterization of the structures 312and 332 as “reinforcement sections,” it should be appreciated that theentire focus of the methodology of FIGS. 15A-G could in fact be tosimply provide a plurality of at least generally laterally extendingetch release conduits, to in turn provide a “rapid etch releasefunction” for the microstructure 302. That is, it is not required thatthe structures 312 and 332 actually structurally reinforce themicrostructure 302, although such is preferably the case. Therefore, thestructures 312 could also be characterized as etch release rails or thelike.

[0168] The basic principle for forming etch release channels or conduitsencompassed by the methodology represented in FIGS. 15A-G is that thedeposition of a sacrificial material onto a layer having at least oneand more typically a plurality slots having a height that is at least asgreat as the width produces a keyholing effect at the bottom of theslot, which in turn defines an etch release channel or conduit. Thelayer with the noted types of slots may exist at various levels withinthe microstructure being fabricated and yet still allow for theformation of etch release channels or conduits in this same generalmanner. Moreover, a layer with the noted types of slots does not need tobe structurally interconnected with the uppermost structural layer ofthe microstructure being fabricated to allow for the formation of etchrelease channels or conduits in this same general manner. For instance,the layer with the noted types of slots instead could be anchored to theunderlying substrate or another underlying structural layer. In fact,this layer with the noted types of slots need not remain in the finalstructure of the microstructure being fabricated at all, but instead maybe removed during the release of the microstructure from the substrate.

[0169] Another method for making another embodiment of a reinforcedmicrostructure 338 is illustrated in FIGS. 16A-C. FIG. 16A illustrates asubstrate 340 on which the microstructure 338 will be fabricated. Afirst sacrificial layer 340 is deposited over the substrate 336. Thefirst sacrificial layer 340 may actually be a plurality of sacrificiallayers that are deposited at different times in the process. In anycase, the first sacrificial layer 340 is patterned to define a pluralityof at least generally laterally extending apertures 344 as illustratedin FIG. 16B. These apertures 344 do not extend down through the entirethickness of the first sacrificial layer 340 in the illustratedembodiment, and may be made by a timed etch. These apertures 344 mayalso be made by first etching down to the substrate 336, and thenbackfilling with a sacrificial material in a subsequent deposition toprovide apertures 344 of the desired depth.

[0170] The apertures 344 effectively function as a mold cavity and maybe in any desired shape for the resulting reinforcing structure. Forinstance, the apertures 344 may be arranged to define a plurality of atleast generally laterally extending ribs or rails (e.g., similar to therails 118 of the mirror microstructure 106 of FIG. 5; the rails 154 or142 of the mirror microstructure 130 of FIG. 7). Another option would beto arrange the apertures 344 to define a waffle pattern, honeycombpattern, hexagonal pattern, or the like (e.g., a grid or network ofreinforcing structures), such as defined by a plurality of intersectingrails that utilized by the mirror microstructure 166 of FIGS. 9A-B.

[0171] A first structural layer 348 is deposited on the firstsacrificial layer 340 as illustrated in FIG. 16C. The first structurallayer 348 extends within and occupies at least substantially theentirety of each of the apertures 344 that were previously formed in thefirst sacrificial layer 340. Those portions of the first structurallayer 348 that are disposed within the apertures 344 may becharacterized as a reinforcement structures 352 that “cantilever” orextend downwardly from the first structural layer 348 at least generallytoward the underlying substrate 336.

[0172] The upper surface of the first structural layer 348 may retain awavy or uneven contour. The upper surface of the first structural layer348 may then be planarized in an appropriate manner, such as by chemicalmechanical polishing, to yield a sufficiently flat upper surface for thefirst support layer 348. Thereafter, the first structural layer 348 isreleased by removing the first sacrificial layer 340. A plurality ofsmall etch release holes (not shown) will extend through the entirevertical extent of the first structural layer 348 to allow for theremoval of the first sacrificial layer 340 that is disposed between thefirst structural layer 348 and the substrate 336. Therefore, the primarybenefit of the design of the microstructure 338 is the structuralreinforcement of the first structural layer 348 and the existence of arelatively large space between the lower extreme of the reinforcingassembly 352 and the substrate 336.

[0173] Another method for making a microstructure is illustrated inFIGS. 17A-G. This methodology may be utilized to make the mirrormicrostructure 106 of FIGS. 5-6, and the principles of this methodologymay be utilized in/adapted for the manufacture of the mirrormicrostructure 30 of FIGS. 2-3, the mirror microstructure 58 of FIG. 4,the mirror microstructure 130 of FIG. 7, the mirror microstructure 384of FIGS. 10A-C, and the mirror microstructure 384′ of FIG. 10D, as wellas the variations therefore that are presented in FIGS. 11A-F. Inaddition to being able to form a desired reinforcing structure, themethodology of FIGS. 17A-G further provides a desired manner forreleasing the microstructure at the end of processing by forming aplurality of at least generally laterally extending etch releaseconduits in one or more of its sacrificial layers to facilitate theremoval thereof to provide the releasing function.

[0174] Multiple layers are first sequentially deposited/formed over anappropriate substrate 448 as illustrated in FIG. 17A, including a firstsacrificial layer 449, a first structural layer 450, and a secondsacrificial layer 454. The second sacrificial layer 454 is thenpatterned to define a plurality of etch release conduit apertures 458 asillustrated in FIG. 17B. These etch release conduit apertures 458 may bein the form of at least generally laterally extending grooves ortrenches, and nonetheless are defined by a pair of at least generallyvertically disposed and spaced sidewalls 462.

[0175] A third sacrificial layer 466 is then deposited on the secondsacrificial layer 454 as illustrated in FIG. 17C. The material thatdefines the third sacrificial layer 466 is also deposited within and atleast substantially fills the etch release conduit apertures 458 thatwere previously formed in the second sacrificial layer 454, and such maybe characterized as being part of the third sacrificial layer 466.Although FIG. 17C shows an intersection between the third sacrificiallayer 466 and the second sacrificial layer 454, typically such anintersection will not exist and instead will at least appear to becontinuous. In any case, that portion of the third sacrificial layer 466that is deposited alongside the sidewalls 462 of the etch releaseconduit apertures 458 will be of a lower density than other portions ofthe third sacrificial layer 466, as well as the second sacrificial layer454 and first sacrificial layer 449 for that matter. These low densityregions ultimately become a plurality of etch release channels as willbe discussed in more detail below. It should be appreciated that thespacing between the sidewalls 462 of each aperture 458 may also besubject to the types of “keyholing” effects discussed above in relationto the methodology of FIGS. 15A-G. That is, in the event that the ratioof the height of the sidewalls 462 of a given etch release conduitaperture 458 to the spacing between these two sidewalls 462 is at leastabout 1:1, an etch release conduit or channel will also develop in thelower portion of this etch release conduit aperture 458 due to the“closing” off of the upper portion of this etch release conduit aperture458 during the deposition of the third sacrificial layer 466.

[0176] The upper surface of the third sacrificial layer 466 may retain awavy or uneven contour, as illustrated in FIG. 17C. Generally, thoseportions of the third sacrificial layer 466 that are disposed over theetch release conduit apertures 458 may be disposed at a lower elevationthan those portions of the third sacrificial layer 466 that are disposedbetween adjacent etch release conduit apertures 458. In the event thatthis is the case and as illustrated in FIG. 17D, the upper surface ofthe third sacrificial layer 466 may be planarized in an appropriatemanner, such as by chemical mechanical polishing, to yield asufficiently flat upper surface for the stack as thus far defined. Thisplanarization may totally eliminate the third sacrificial layer 466except from within the etch release conduit apertures 458 as shown, orthe third sacrificial layer 466 may remain as a continuous layer on thefirst sacrificial layer 454 (not shown, but in the manner depicted inFIG. 19D discussed below).

[0177] Reinforcement structures may be incorporated into themicrostructure using the method of FIGS. 17A-G. In this regard, thesecond sacrificial layer 454, as well as any overlying portion of thethird sacrificial layer 466, may be patterned to define a plurality ofinterconnect apertures 470 as illustrated in FIG. 17E. Notably, theseinterconnect apertures 470 are disposed between the etch release conduitapertures 458 that now have the material of the third sacrificial layer466 therein. That is, preferably none of the interconnect apertures 470extend downwardly through and/or intersect any of the etch releaseconduit apertures 458 that now include material from the thirdsacrificial layer 466. These interconnect apertures 470 allow forestablishing a structural interconnection with the first structurallayer 450, and may be in various forms. For instance, these interconnectapertures 470 may be in the form of at least generally laterallyextending grooves or trenches (e.g., to define a plurality of rails orat least the upper portion thereof and of the type utilized by themicrostructure 106 of FIG. 5 and the microstructure 130 of FIG. 7, aswell as the variations therefore illustrated in FIGS. 11A-F), or may bein the form of a plurality of separate and discrete holes that aredisposed in spaced relation (e.g., to define a plurality of posts orcolumns of the type utilized by the mirror microstructure 30 of FIGS.2-3).

[0178] A second structural layer 474 is deposited on any exposedportions of the second sacrificial layer 454 and the third sacrificiallayer 466, as illustrated in FIG. 17F. The material that defines thesecond structural layer 474 is also deposited within and at leastsubstantially fills the interconnect apertures 470 within the secondsacrificial layer 454, and such may be characterized as being part ofthe second structural layer 474. This portion of the second structurallayer 474 may be characterized as a plurality of reinforcement sections478 for the microstructure 476 that is being fabricated. Although FIG.17F shows an intersection between the lower extreme of each of thereinforcement sections 478 and the upper extreme of first structurallayer 450, typically such an intersection will not exist and insteadwill at least appear to be continuous.

[0179] The upper surface of the second structural layer 474 may retainhave a wavy or uneven contour. Generally, those portions of the secondstructural layer 474 that are disposed over the reinforcement sections478 may be recessed to a degree. Therefore, the upper surface of thesecond structural layer 474 may be planarized in an appropriate manner,such as by chemical mechanical polishing, to yield a sufficiently flatupper surface for the second structural layer 474 and as illustrated inFIG. 17F. This completes the definition of the microstructure 476. Itshould be appreciated that the system that includes the microstructure476 will likely include other components than those illustrated in FIGS.17A-G and that may interface with the microstructure 476 in some manner(e.g., one or more actuators). Moreover, it should be appreciated thatthe steps illustrated in FIGS. 17A-G may be repeated in an appropriatemanner in order to define a microstructure of the type presented inFIGS. 4 and 7 (e.g., three or more spaced, but structurallyinterconnected, structural layers).

[0180] The microstructure 476 is now ready to be released. “Released”means to remove each of the sacrificial layers of the surfacemicromachined system and thereby including the first sacrificial layer449, the second sacrificial layer 454, and the third sacrificial layer466. An etchant is used to provide the releasing function. The manner inwhich the microstructure 476 was formed in accordance with themethodology of FIGS. 17A-G reduces the time required for the sacrificiallayers 454 and 466 to be totally removed. Ultimately, a plurality of atleast generally laterally extending etchant flow pipes, channels, orconduits are formed in the third sacrificial layer 466. Those portionsof the third sacrificial layer 466 that are positioned alongside thesidewalls 462 of the etch release conduit apertures 458 that were formedin the second sacrificial layer 454 are less dense than the remainder ofthe third sacrificial layer 466. The etch rate will be greater in thelow density regions of the third sacrificial layer 466 than throughoutthe remainder of the third sacrificial layer 466. This will effectivelyform an etch release pipe, channel or conduit in the third sacrificiallayer 466 along each sidewall 462. The development of the etch releasechannels during the initial portion of the release etch provides accessto radially inwardly disposed locations within the sacrificial layersfor the etchant to complete the release before the etchant has anysignificant adverse effect on the microstructure 476.

[0181] The methodology represented by FIGS. 17A-G provides a number ofadvantages. One is that the first sacrificial layer 454 may be patternedto define any appropriate arrangement for the etch release conduitapertures 458 within/throughout a sacrificial layer(s) (and thereby anarrangement for the low density regions which will ultimately define theetch release conduits), including an arrangement where one or more ofthese etch release conduit apertures 458 intersect. That is, theformation of the etch release conduits is not adversely affected byhaving the low density regions intersect.

[0182] FIGS. 18A-B present one arrangement where the first sacrificiallayer 454 has been patterned to define a network 482 or grid of oneembodiment of intersecting/interconnected etch release conduit apertures458. The network 482 of intersecting/interconnected etch release conduitapertures 458 increases the amount of the sacrificial layer that isinitially exposed to the release etchant within radially inwardlocations, and thereby should reduce the total amount of time requiredto release the microstructure 476 that is being formed. The various etchrelease conduit apertures 458 may be routed to define a desired network482 for distribution of the release etchant throughout the firstsacrificial layer 454 to not only reduce this total etch release time,but to also allow for use of a desired reinforcing structure. In thisregard, FIG. 18B illustrates one embodiment that may be used for thereinforcement sections 478 in combination with the network 482 of FIG.18A. The reinforcement sections 478 of FIG. 18B are in the form of aplurality of spaced posts or columns that structurally interconnect thefirst structural layer 450 and the second structural layer 474 of themicrostructure 459 (e.g., for defining a microstructure of the typeillustrated in FIG. 2A).

[0183] Another advantage associated with the manner in which the etchrelease conduits are formed in the methodology of FIGS. 17A-G, is thatthese etch release conduits may be formed without requiring the use ofany reinforcement structures. This is illustrated by the sequential viewpresented in FIGS. 19A-F. Multiple layers are sequentiallydeposited/formed over an appropriate substrate 488, including a firstsacrificial layer 490 as illustrated in FIG. 19A. The first sacrificiallayer 490 is then patterned to define a plurality of etch releaseconduit apertures 492 as illustrated in FIG. 19B. These etch releaseconduit apertures 492 may be of the type used by the methodology ofFIGS. 17A-G, and are defined by a pair of at least generally verticallydisposed and spaced sidewalls 494.

[0184] A second sacrificial layer 496 is then deposited on the firstsacrificial layer 490, as illustrated in FIG. 19C. The material thatdefines the second sacrificial layer 496 is also deposited within and atleast substantially fills the etch release conduit apertures 492 thatwere previously formed in the first sacrificial layer 490, and such maybe characterized as being part of the second sacrificial layer 496.Although FIG. 19C shows an intersection between the second sacrificiallayer 496 and the third sacrificial layer 490, typically such anintersection will not exist and instead will at least appear to becontinuous. In any case, that portion of the second sacrificial layer496 that is deposited alongside the sidewalls 494 of the etch releaseconduit apertures 492 will be of a lower density than other portions ofthe second sacrificial layer 496, as well as the first sacrificial layer490 for that matter.

[0185] The upper surface of the second sacrificial layer 496 may retaina wavy or uneven contour, as illustrated in FIG. 19C. The upper surfaceof the second sacrificial layer 496 may be planarized in an appropriatemanner, such as by chemical mechanical polishing, to yield asufficiently flat upper surface for the stack as thus far defined and asillustrated in FIG. 19D. This planarization may totally eliminate thesecond sacrificial layer 496 except from within the etch release conduitapertures 492 (not shown), or the second sacrificial layer 496 mayremain as a continuous layer on the first sacrificial layer 490 as shownin FIG. 19D.

[0186] A first structural layer 498 is then deposited on any exposedportions of the first sacrificial layer 490 and the second sacrificiallayer 496, as illustrated in FIG. 19E. This completes the definition ofthe microstructure 486. It should be appreciated that the system thatincludes the microstructure 486 will likely include other componentsthan those illustrated in FIGS. 19A-F and that may interface with themicrostructure 486 in some manner (e.g., one or more actuators).

[0187] The microstructure 486 is now ready to be released. “Released”means to remove each of the sacrificial layers of the surfacemicromachined system and thereby including the first sacrificial layer490 and the second sacrificial layer 496. An etchant is used to providethe releasing function. The manner in which the microstructure 486 wasformed in accordance with the methodology of FIGS. 19A-F reduces thetime required for the sacrificial layers 490 and 496 to be totallyremoved. Ultimately, a plurality of at least generally laterallyextending etchant flow pipes, channels, or conduits are formed in thesecond sacrificial layer 496. Those portions of the second sacrificiallayer 496 that are positioned alongside the sidewalls 494 of the etchrelease conduit apertures 492 that were formed in the first sacrificiallayer 490 are less dense than the remainder of the second sacrificiallayer 496. The etch rate will be greater in the low density regions ofthe second sacrificial layer 496 than throughout the remainder of thesecond sacrificial layer 496. This will effectively form an etch releasepipe, channel or conduit in the second sacrificial layer 496 along eachsidewall 494. The development of the etch release channels during theinitial portion of the release etch provides access to radially inwardlydisposed locations within the sacrificial layers for the etchant tocomplete the release before the etchant has any significant adverseeffect on the microstructure 486.

[0188] Etch release channels that exist prior to the release of themicrostructure 486 may also be formed by the “keyholing” conceptdiscussed above in relation to FIGS. 15A-G. Generally, a relationshipbetween the width of the etch release conduit apertures 492 and theheight or vertical extent of these etch release conduit apertures 492may be selected to allow a plurality of etch release channels to bedefined in the lower portion of these apertures 492. When thisrelationship is selected in the same general manner discussed above inrelation to FIGS. 15A-G, the second sacrificial layer 496 will extendwithin and occupy only a portion of each of the apertures 492 that werepreviously formed from the first sacrificial layer 490. However, thematerial that defines the second sacrificial layer 496 will not fill oroccupy the entirety of the apertures 492 due to the relative closespacing between the sidewalls 494 that define the etch release conduitapertures 492 in relation to the height or vertical extent of theseapertures 492 (i.e., a void will remain in the lower portion of eachaperture 492). This again may be characterized as “keyholing.” In anycase, the remaining voids in the lower portion of each of the etchrelease conduit apertures 492 will define a plurality of at leastgenerally laterally extending etch release channels.

[0189] Another method for making a microstructure is illustrated byreference to FIGS. 20A-D. The fundamental principles of this methodologymay be utilized to make the mirror microstructure 30 of FIG. 2A, themirror microstructure 58 of FIG. 4, the mirror microstructure 106 ofFIGS. 5-6, the mirror microstructure 130 of FIG. 7, the mirrormicrostructure 384 of FIGS. 10A-C, the mirror microstructure 384′ ofFIG. 10D, as well as the variations therefore that are presented inFIGS. 11A-F. In addition to accommodating the fabrication of at leastcertain types of reinforcing structures for the microstructure, themethodology embodied by FIGS. 20A-D further provides a desired mannerfor releasing the microstructure at the end of fabrication by forming aplurality of at least one at least generally laterally extending etchrelease conduit within one or more of its sacrificial layers tofacilitate the removal of this sacrificial material during the releaseof the microstructure from the substrate.

[0190] Multiple layers of at least two different types of materials aresequentially deposited to define a stack 594 on a substrate 582 that isappropriate for surface micromachining. The various deposition andpatterning steps that may yield the configuration illustrated in FIG.20A have been sufficiently described in relation to other embodiments,and will not be repeated. The stack 594 includes a microstructure 592,which in the illustrated embodiment is in the form of a singlestructural layer 590 that is disposed in spaced relation to thesubstrate 582. Any configuration that is appropriate for the manner ofdefining etch release channels in the manner contemplated by FIGS. 20A-Dmay be utilized for the microstructure 592, including where thestructural layer 590 is structurally reinforced in an appropriatemanner. In any case, the stack 594 also includes an etch release conduitfill material 586 that is encased within a sacrificial material 584 bothwithin the area occupied by the microstructure 592 and laterally beyondthe microstructure 592 or “off to the side” of the microstructure 592.Generally, this etch release conduit fill material 586 is removed by afirst etchant to form at least one laterally extending etch releaseconduit 602 at least somewhere underneath at least one structural layerof the microstructure 592. That is, the first etchant is more selectiveto the etch release conduit fill material 586 than the sacrificialmaterial 584 in an amount such that it does not remove any significantportion of the sacrificial material 584. Thereafter, a second, differentetchant (i.e., a release etchant) enters the etch release conduit(s)602. This second, different etchant removes at least that portion of thesacrificial material 584 which is accessible through the etch releaseconduit(s) 602 to release the microstructure 592 from the substrate 582.That is, the second etchant is more selective to the sacrificialmaterial 584 than the structural layer 590 in an amount such that itdoes not remove any significant portion of the structural layer 590.

[0191] The etch release conduit fill material 586 may be disposed at oneor more levels relative to the substrate 582 within the microstructure592. An at least generally vertically extending runner 588 of etchrelease conduit material 586 is disposed laterally beyond the areaoccupied by the microstructure 592 (i.e., off to the side), and extendsat least generally downwardly from an uppermost exterior surface 596 ofthe stack 594 toward the substrate 582 to the etch release conduit fillmaterial 586 at one or more of the levels within the stack 594. Anyappropriate number of runners 588 may be utilized, and each may be ofany appropriate configuration.

[0192] The etch release conduit fill material 586 at any level withinthe stack 594 may occupy the entirety of this level under at least onestructural layer of the microstructure 592. More typically, a patterningoperation will have been done at a given level to define an appropriatelayout of etch release rails from the etch release conduit fill material586. FIG. 20B illustrates one embodiment of a layout of etch releaserails 598 of etch release conduit fill material 586 that are in the formof a grid or network. Other layouts for the etch release rails 598 maybe utilized, including without limitation those discussed above. In thecase of the embodiment of FIG. 20B, sacrificial material 584 is alsodisposed at the same level within the stack 594 as the etch releaserails 598 (i.e., in the space between adjacent etch release rails 598).Reinforcement structures 600 also may be disposed at the same levelwithin the stack 594 as the etch release rails 598 in this same space aswell if desired. These reinforcement structures 600 are separated fromthe etch release conduit fill material 586 by sacrificial material 584.That is, the etch release conduit fill material 584 is encased withinsacrificial material 584.

[0193] Regardless of the layout of the etch release rails 598 of etchrelease conduit fill material 586, the microstructure 592 is released inthe same general manner. Initially, the stack 594 is exposed to a firstetchant that is selective to the etch release conduit fill material 586.In one embodiment, the etch release conduit fill material 586 is thesame material that is used to form the various structural layers thatdefine the microstructure 592. In this case, it is necessary for thevarious structural layers of the microstructure 592 to be isolated fromthe etch release conduit fill material 586 by sacrificial material 584.There may be instances where a particular etchant may be sufficientlyselective to the etch release conduit fill material 586 so as to notrequire this isolation of the structural material of the microstructure592 from the etch release conduit fill material 586. The first etchantremoves the etch release conduit fill material 586 within the runner 588to define an access 604, as well as any etch release rails 598 of etchrelease conduit fill material 586 connected therewith. This firstetchant preferably does not remove any significant portion of anysacrificial material 584 that encases the etch release rails 598 and/orthe runner(s) 588. The resulting void by this removal of material of theetch release rails 598 defines at least one etch release conduit 602that is at least generally laterally extending and disposed under atleast one structural layer of the microstructure 592 (FIG. 20C). In thelayout of etch release rails 598 illustrated in FIG. 20B, there would bea grid or network of etch release conduits 602 within the sacrificialmaterial 584 disposed under the area occupied by the structural layer590.

[0194] There is a separate and distinct second etching operation inaccordance with the methodology of FIGS. 20A-D. After the first etchingoperation has been executed to define at least one and more typically aplurality of etch release conduits 602, the stack 594 undergoes a secondetching operation. The second etching operation uses a second etchantthat is different from the first etchant, and that is selective to thesacrificial material 584. This second etchant flows down through thevarious accesses 604 that may be associated with the stack 594 and intoany etch release conduit 602 fluidly interconnected therewith. Thesecond etchant removes any sacrificial material 584 in contact therewithto release the microstructure 592 from the substrate 582 (FIG. 20D). Inthe event that the etch release conduit fill material 586 ispolysilicon, representative examples for the first etchant would bepotassium hydroxide, methylammonium hydroxide, and xenon difluoride.Assuming that the sacrificial material 584 is doped or undoped siliconedioxide or silicone oxide, representative examples for the secondetchant would be HF-based, including those identified above.

[0195] The foregoing description of the present invention has beenpresented for purposes of illustration and description. Furthermore, thedescription is not intended to limit the invention to the form disclosedherein. Consequently, variations and modifications commensurate with theabove teachings, and skill and knowledge of the relevant art, are withinthe scope of the present invention. The embodiments describedhereinabove are further intended to explain best modes known ofpracticing the invention and to enable others skilled in the art toutilize the invention in such, or other embodiments and with variousmodifications required by the particular application(s) or use(s) of thepresent invention. It is intended that the appended claims be construedto include alternative embodiments to the extent permitted by the priorart.

What is claimed is:
 1. A method for making a surface micromachinedmicrostructure, comprising the steps of: forming a first sacrificiallayer over a first substrate, wherein a lateral dimension is at leastgenerally parallel with an upper surface of said first substrate;forming a plurality of discrete and at least generally laterallyextending hollow conduits that are defined at least in part by saidfirst sacrificial layer; forming a first structural layer over saidfirst sacrificial layer; and removing said first sacrificial layer,wherein said removing step comprises flowing an etchant within at leastsome of said plurality of conduits.
 2. A method, as claimed in claim 1,wherein: each of said forming a first sacrificial layer step and saidforming a first structural layer step is selected from the groupconsisting of chemical vapor deposition, thermal oxidation processes,physical vapor deposition, and any combination thereof.
 3. A method, asclaimed in claim 1, wherein: said forming a plurality of conduits stepcomprises: forming a first intermediate layer on said first sacrificiallayer before said forming a first structural layer step, whereby saidfirst intermediate layer is thereby disposed somewhere between saidfirst structural layer and said first substrate; patterning said firstintermediate layer into a first subassembly; etching only an upperportion of said first sacrificial layer after said patterning step,wherein said etching step comprises forming undercuts beneath edgeportions of said first subassembly; and forming a second sacrificiallayer at least on said first sacrificial layer, wherein said forming asecond sacrificial layer step is executed after said etching step, andwherein said forming a second sacrificial layer step fails to fill saidundercuts and which thereby defines said plurality of conduits.
 4. Amethod, as claimed in claim 3, wherein: said forming a firstintermediate layer step comprises forming a first intermediatestructural layer.
 5. A method, as claimed in claim 3, wherein: saidfirst subassembly remains after said removing step.
 6. A method, asclaimed in claim 3, wherein: said forming a second sacrificial layerstep further comprises forming said second sacrificial layer on and overan entirety of said first subassembly.
 7. A method, as claimed in claim6, further comprising the step(s) of: planarizing an upper surface ofsaid second sacrificial layer; and etching entirely through said secondsacrificial layer to said first subassembly to define a firstinterconnect aperture assembly in said second sacrificial layer thatexposes said first subassembly, wherein said forming a first structurallayer step comprises depositing a structural material both within saidfirst interconnect aperture assembly and on top of said secondsacrificial layer.
 8. A method, as claimed in claim 7, wherein: apattern of said first interconnect aperture assembly in said secondsacrificial layer at least generally matches a pattern of said firstsubassembly.
 9. A method, as claimed in claim 7, wherein: said firstinterconnect aperture assembly comprises a plurality of separate anddiscrete holes that are disposed in spaced relation to each other.
 10. Amethod, as claimed in claim 7, wherein: said first subassembly comprisesa plurality of laterally extending strips.
 11. A method, as claimed inclaim 7, wherein: said planarizing step comprises chemical mechanicalpolishing.
 12. A method, as claimed in claim 7, wherein: said forming afirst structural layer step comprises forming a depression on an upper osurface of first structural layer which is vertically aligned with wheresaid structural material was deposited within said first interconnectaperture assembly, and wherein said method further comprises the step ofplanarizing said upper surface of said first structural layer.
 13. Amethod, as claimed in claim 6, wherein: said forming a first structurallayer step is executed after said forming a second sacrificial layerstep, whereby said second sacrificial layer a disposed somewhere betweensaid first structural layer and said first substrate, said methodfurther comprising the step of: structurally interconnecting said firststructural layer and said first subassembly through said secondsacrificial layer and before execution of said removing step.
 14. Amethod, as claimed in claim 3, wherein: each of said first structurallayer and said first intermediate layer consist of polysilicon.
 15. Amethod, as claimed in claim 3, wherein: said removing step furthercomprises removing said first subassembly using said etchant.
 16. Amethod, as claimed in claim 15, wherein: a maximum thickness of saidfirst subassembly is about 1500 Å.
 17. A method, as claimed in claim 15,wherein: said first subassembly consists of silicon nitride.
 18. Amethod, as claimed in claim 3, wherein: said first subassembly consistsof a plurality of at least generally laterally extending strips.
 19. Amethod, as claimed in claim 3, wherein: said forming a first structurallayer step is executed after said forming a second sacrificial layerstep, whereby said second sacrificial layer is disposed at leastsomewhere between said first structural layer and said first substrate.20. A method, as claimed in claim 3, wherein: said removing step furthercomprises removing second sacrificial layer.
 21. A method, as claimed inclaim 1, further comprising the steps of: forming a first intermediatelayer between said first sacrificial layer and said first structurallayer, whereby said first intermediate layer is disposed at leastsomewhere between said first sacrificial layer and said first structurallayer; patterning said first intermediate layer into a plurality of atleast generally laterally disposed and axially extending strips that aredisposed in at least substantially parallel and equally spaced relation,wherein a maximum spacing between adjacent pairs of said plurality ofstrips is about 1.5 microns, and wherein a minimum thickness of each ofsaid plurality of strips is about 1.5 microns; forming said firstsacrificial layer over said first intermediate layer, wherein saidforming said first sacrificial layer step fails to fill an entirety ofsaid spacing between said adjacent pairs of said plurality of strips andwhich thereby defines said plurality of conduits.
 22. A method, asclaimed in claim 1, wherein: said forming a plurality of conduits stepis executed before said forming a first structural layer step.
 23. Amethod, as claimed in claim 1, further comprising the step of: formingat least one intermediate sacrificial layer and at least oneintermediate structural layer between said first sacrificial layer andsaid first substrate.
 24. A method, as claimed in claim 1, wherein: saidfirst structural layer is free of any aperture which at any time extendsentirely downwardly through said first structural layer.
 25. A method,as claimed in claim 1, wherein: said first structural layer is movablerelative to said first substrate after said removing step.
 26. A method,as claimed in claim 1, wherein: said forming a plurality of discrete andat least generally laterally extending hollow conduits step comprisesdisposing said plurality of hollow conduits in non-intersectingrelation.
 27. A method, as claimed in claim 1, wherein: said forming aplurality of discrete and at least generally laterally extending hollowconduits step comprises disposing said plurality of hollow conduits inat least substantially parallel relation.
 28. A method, as claimed inclaim 27, wherein: said forming a plurality of discrete and at leastgenerally laterally extending hollow conduits step further comprisesdisposing said plurality of hollow conduits in at least substantiallyequally spaced relation.
 29. A method, as claimed in claim 1, wherein:said forming a plurality of discrete and at least generally laterallyextending hollow conduits step further comprises directing a first pairof said hollow conduits at least generally toward a first common pointand directing a second pair of said hollow conduits at least generallytoward a second common point which is different from said first commonpoint.
 30. A method, as claimed in claim 1, wherein: said forming aplurality of discrete and at least generally laterally extending hollowconduits step further comprises disposing each of said plurality ofhollow conduits so as to be at least generally radially extending inrelation to a common center.
 31. A method, as claimed in claim 30,wherein: each of said plurality of hollow conduits terminates at leastat generally the same location in proximity to but not at said commoncenter.
 32. A method, as claimed in claim 30, wherein: a first saidhollow conduit extends closer to said common center than a second saidhollow conduit.
 33. A method, as claimed in claim 1, wherein: saidforming a plurality of discrete and at least generally laterallyextending hollow conduits step comprises forming each of said pluralityof hollow conduits in and at least substantially axially extendingconfiguration.
 34. A method, as claimed in claim 1, wherein: saidforming a plurality of discrete and at least generally laterallyextending hollow conduits step comprises forming each of said pluralityof hollow conduits in other than an axially extending configuration. 35.A method, as claimed in claim 1, wherein: said forming a plurality ofdiscrete and at least generally laterally extending hollow conduits stepcomprises forming each of said plurality of hollow conduits in an atleast generally a sinusoidal configuration.
 36. A method, as claimed inclaim 1, wherein: said forming a plurality of discrete and at leastgenerally laterally extending hollow conduits step comprises using afirst etchant that is not selective to said first sacrificial layer, andwherein said removing step comprises using a second etchant that isselective to said first sacrificial layer.
 37. A method, as claimed inclaim 1, wherein: said forming a plurality of discrete and at leastgenerally laterally extending hollow conduits step comprises encasing aplurality of etch release rails within said first sacrificial layer andremoving said etch release rails without removing said first sacrificiallayer.
 38. A method, as claimed in claim 37, wherein: a stack comprisessaid first sacrificial layer, said first structural layer, said firstsubstrate, and a first exterior surface that is disposed opposite saidfirst substrate, wherein said method further comprises the step offorming a first runner that is laterally spaced from said firststructural layer, that extends from said first exterior surface at leasttoward said substrate, and that is interconnected with at least one ofsaid plurality of etch release rails, wherein said removing said etchrelease rails further comprises first removing said first runner andthen each said etch release rail that is interconnected with said firstrunner.
 39. A method for making a surface micromachined microstructure,comprising the steps of: forming a first sacrificial layer over a firstsubstrate; forming a first intermediate layer on said first sacrificiallayer; forming a plurality of first strips from said first intermediatelayer that are disposed on and extend at least generally laterallyrelative to said first sacrificial layer; forming a second sacrificiallayer on said first sacrificial layer and at least alongside each ofsaid plurality of first strips; forming a first structural layer oversaid second sacrificial layer; and removing said first and secondsacrificial layers, wherein said removing step comprises etching saidfirst and second sacrificial layers, and wherein said etching stepcomprises etching said second sacrificial layer at a greater rate withineach portion of said second sacrificial layer which interfaces with anyportion of said first strips in comparison to portions of said secondsacrificial layer which are free from contact with any portion of any ofsaid plurality of first strips.
 40. A method, as claimed in claim 39,wherein: said forming a second sacrificial layer step further comprisesforming said second sacrificial layer on and over each of said pluralityof first strips.
 41. A method, as claimed in claim 40, wherein: saidfirst strips are structural and remain after execution of said removingstep, wherein said method further comprises the step of structurallyinterconnecting said first strips and said first structural layerthrough said second sacrificial layer and before execution of saidremoving step.
 42. A method, as claimed in claim 39, wherein: said firststrips are structural and remain after execution of said removing step,wherein said method further comprises the steps of: planarizing an uppersurface of said second sacrificial layer; etching through said secondsacrificial layer to each of said plurality of first strips to define afirst interconnect aperture assembly in said second sacrificial layer,wherein said forming a first structural layer step is executed aftersaid etching through said second sacrificial layer step to expose eachof said plurality of first strips, and wherein said forming a firststructural layer step comprises depositing structural material bothwithin said first interconnect aperture assembly and on top of saidsecond sacrificial layer.
 43. A method, as claimed in claim 42, wherein:a pattern of said first interconnect aperture assembly in said secondsacrificial layer at least generally matches a pattern of said firststrips.
 44. A method, as claimed in claim 42, wherein: said firstinterconnect aperture assembly comprises a plurality of separate anddiscrete holes that are disposed in spaced relation to each other.
 45. Amethod, as claimed in claim 42, wherein: said plurality of first stripsare further disposed in at least one of non-intersecting relation,parallel relation, radial relation, intersecting relation, and anycombination thereof.
 46. A method, as claimed in claim 42, wherein: saidplanarizing step comprises chemical mechanical polishing.
 47. A method,as claimed in claim 42, wherein: said forming a first structural layerstep comprises forming a depression on an upper surface of firststructural layer which is vertically aligned with where said structuralmaterial was deposited within said first interconnect aperture assembly,and wherein said method further comprises the step of planarizing saidupper surface of said first structural layer.
 48. A method, as claimedin claim 39, wherein: said forming a plurality of first strips stepcomprises disposing said plurality of first strips in at leastsubstantially parallel relation.
 49. A method, as claimed in claim 48,wherein: said forming a plurality of first strips step comprisesdisposing said plurality of first strips in at least substantiallyequally spaced relation.
 50. A method, as claimed in claim 48, wherein:said forming a plurality of first strips step comprises disposing afirst pair of adjacent said first strips so as to be directed at leastgenerally toward a first common point and directing a second pair ofsaid first strips at least generally toward a second common point whichis different from said first common point.
 51. A method, as claimed inclaim 39, wherein: said forming a plurality of first strips stepcomprises disposing each of said plurality of first strips so as to beat least generally radially extending in relation to a common center.52. A method, as claimed in claim 51, wherein: each of said plurality offirst strips terminates at least at generally the same location inproximity to but not at said common center.
 53. A method, as claimed inclaim 51, wherein: a first said first strip extends closer to saidcommon center than a second said first strip.
 54. A method, as claimedin claim 39, wherein: said forming a plurality of first strips stepcomprises disposing each of said plurality of first strips in an atleast substantially axially extending configuration.
 55. A method, asclaimed in claim 39, wherein: said forming a plurality of first stripsstep comprises disposing each of said plurality of first strips in otherthan an axially extending configuration.
 56. A method, as claimed inclaim 39, wherein: said forming a plurality of first strips stepcomprises forming each of said plurality of first strips in an at leastgenerally sinusoidal configuration.
 57. A method, as claimed in claim39, wherein: said forming a plurality of first strips step comprisespatterning said first intermediate layer.
 58. A method for making asurface micromachined microstructure, comprising the steps of: forming afirst sacrificial layer over a first substrate, wherein said forming afirst sacrificial layer step comprises forming a plurality of at leastgenerally laterally extending low density regions within said firstsacrificial layer; forming a first structural layer over said firstsacrificial layer; and removing said first sacrificial layer, whereinsaid removing step comprises etching said first sacrificial layer, andwherein said etching step comprises etching said first sacrificial layerat a greater rate within each of said plurality of low density regionsthan outside said plurality of low density regions.
 59. A method, asclaimed in claim 58, further comprising the steps of: forming a firstintermediate layer over said first substrate, wherein said firstintermediate layer is disposed between said first sacrificial layer andsaid first substrate; and patterning said first intermediate layer intoa plurality of first strips, wherein said plurality of first strips areat least generally laterally extending, wherein said forming a firstsacrificial layer step is executed after said patterning step and so asto dispose said first sacrificial layer at least alongside each of saidplurality of first strips, wherein said plurality of low density regionsexist alongside each of said plurality of first strips.
 60. A method, asclaimed in claim 58, further comprising the steps of: forming a secondsacrificial layer over said first substrate; patterning said secondsacrificial layer to define a plurality of at least generally laterallyextending apertures, wherein each said aperture comprises first andsecond aperture sidewalls that are disposed in spaced relation, whereinsaid forming a first sacrificial layer step is executed after saidpatterning step such that at least a portion of said first sacrificiallayer is disposed within each of said plurality of apertures, andwherein said plurality of low density regions exist along said first andsecond sidewalls.
 61. A method, as claimed in claim 60, wherein: saidplurality of apertures are disposed in non-intersecting relation.
 62. Amethod, as claimed in claim 60, wherein: said plurality of aperturesdefine a network of interconnected said apertures.
 63. A method formaking a surface micromachined microstructure, comprising the steps of:forming a first sacrificial layer over a first substrate; forming afirst structural layer over said first sacrificial layer; and removingsaid first sacrificial layer, wherein said removing step comprises usinga first etchant to define at least one etch release channel within saidfirst sacrificial layer and thereafter using a second etchant that isdifferent from said first etchant to remove said first sacrificial layerby allowing said second etchant to flow within said at least one etchrelease channel.
 64. A method, as claimed in claim 63, wherein: saidfirst etchant is not selective to said first sacrificial layer, andwherein said second etchant is selective to said first sacrificiallayer.
 65. A method, as claimed in claim 63, further comprising the stepof: encasing a plurality of etch release rails within said firstsacrificial layer, wherein said using a first etchant comprises removingsaid etch release rails without removing said first sacrificial layer.66. A method, as claimed in claim 65, wherein: a stack comprises saidfirst sacrificial layer, said first structural layer, said firstsubstrate, and a first exterior surface that is disposed opposite saidfirst substrate, wherein said method further comprises the step offorming a first runner that is laterally spaced from said firststructural layer, that extends from said first exterior surface at leasttoward said substrate, and that is interconnected with at least one ofsaid plurality of etch release rails, wherein said removing said etchrelease rails further comprises first removing said first runner andthen each said etch release rail that is interconnected with said firstrunner.